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UNITED STATES OE AMEEICA. 






STEAM BOILER 



EXPLOSIONS, 



IN THEORY AND IN PRACTICE; 



BY 



R. H. THURSTON, M.A., Doc. Eng, 

DIRECTOR OF THE SIBLEY COLLEGE, CORNELL UNIVERSITY 

AUTHOR OF A HISTORY OF THE STEAM ENGINE; 

STATIONARY STEAM ENGINES; MATERIALS 

OF ENGINEERING, ETC., ETC., ETC. 



1 H 



WELL LLLUSTRATED. 



NEW YORK. 

JOHN WILEY & SONS 

1887. 







Copyright 1887, by ROBERT H. THURSTON, 



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Frank Williams, Printer and Electrotype^ 
62 Duane St., N. Y. 



PREFACE. 



This little treatise on Steam-Boiler Explosions had its 
origin in the following circumstances : 

In the year 1872 the Author received from the Secretary 
of the Treasury of the United States a communication in 
which he w r as requested to prepare, for the use of the 
Treasury Department, a report on the causes and the con- 
ditions leading to the explosions of steam-boilers, and 
began the preparation of such a report, in which he pro- 
posed to incorporate the facts to be here presented. 

The pressure of more imperative duties became so 
heavy, immediately after the receipt of that request, that 
the work was interrupted before it had been more than 
fairly begun. An examination had been made of the 
records of earlier legislation, in the United States and in 
foreign countries, relating to the regulation of the use of 
steam boilers ; and an investigation was begun tracing the 
experimental and scientific development of the later the- 
ories of explosion. The work was never entirely given up 
however, and the notes collected from time to time were 
added to those then obtained, and have since formed the 
basis of later lectures by the Author on this subject. 

In the year 1875, the Author, then a member of a com- 
mission formed by the government to investigate the sub- 
ject, was asked by the Cabinet officer having direction of 



} v PREFACE. 

the matter to accept the chairmanship of the commission 
and to give his time to the subject under investigation. 
For sufficient reasons he was unwilling to undertake the 
work, and an older and wiser head was appointed. His 
connection with that commission, however, further stimu- 
lated that interest which he had always felt in the matter, 
and led to the study of the subject from new standpoints. 
It seemed evident, from what was learned there and else- 
where, in the experimental explosion of steam-boilers, that, 
usually, the only unknown element in such cases was the 
magnitude of the stock of energy stored in a boiler before 
explosion, and the extent to which it was applied, at the 
instant of the catastrophe, to the production of disastrous 
effects. 

The calculation of the quantity of energy stored and 
available was undertaken and partly completed, and then 
was interrupted by the decease of a most efficient and help- 
ful assistant ; was again undertaken, later, by two earnest 
friends and pupils of the Author, and was finally completed 
in the form in which it will be found presented in the fol- 
lowing pages. 

Thus, the subject is one which the Author has endeavored 
at several different periods in the course of his work to 
take up and reduce, if possible, to a consistent theoretical 
and practically applicable form. On each occasion his 
labors were interrupted before they were fairly begun. 
It cannot be said that they are now completed ; but 
enough has been done to permit the presentation of a sys- 
tematic outline of this subject. Probably no subject within 
the whole range of the practice of the engineer has de- 
manded or has received more attention than this; and prob- 
ably no such subject has been less satisfactorily developed in 



PRE FA CE. V 

theory and less thoroughly investigated experimentally than 
this. But some good work has now been done, and well done, 
during late years, and the experience of the steam-boiler 
insurance and inspection companies has fortunately served 
an excellent purpose in showing that the element of mys- 
tery commonly exists only in the imagination of writers hav- 
ing more poetry than logic in their composition, and that 
the causes of accident are wholly preventible and controlU 
able. 

R. H. T 



CONTENTS. 



INTRODUCTION. 

Art. Page 

Heat Energy of Water and Steam - 3 

1. The Stored Energy of the Fluid 3 

2. Formulas for Energy Stored - 4 

3. Calculated Quantities of Energy and Tables 8 

4. Deductions from Calculations - - - 12 

5. Curves of Energy 15 

STEAM BOILER EXPLOSIONS. 

6. Character of Explosions 17 

7. Energy Stored in Steam Boilers 23 

8. Energy of Steam Alone - - - - 32 

9. Explosion Distinguished from Bursting - 34 

10. Causes of Explosions - 36 

11. Statistics of Boiler Explosions 41 

12. Theories and Methods - - - - 47 

13. Colburn and Clark's Theory 49 

14. Corroboratory Evidence 52 

15 Energy in Heated Metal 61 

16. Strength of Heated Metal - - - - 63 

17. Low Water and its Effects - 63 

18. Sediment and Incrustation - - - - 73 

19. Energy in Super-Heated Water 78 

20. The Spheroidal St e 86 



CONTENTS. vn 

21 Steady Increase of Pressure 94 

22 Relative Safeey of Boilers - - - - 98 
23. Defective Design . . . . 100 
24 Defective Construction • 105 

25. Developed Weakness; Multiple Explosions - no 

26. General and Local Decay - - - - 114 

27. Methods of Decay ------ 117 

28. Temperature Changes - • - - - 122 

29. Management - 125 

30. Emergencies 128 

31. Results of Explosions - - - - T 3 J 

32. Experimental Investigations - - - 156 

33. Conclusions; Preventives - 168 



INTRODUCTION.* 



HEAT-ENERGY OF STEAM AND WATER. 

I. The Stored Energy of Steam or Water, con- 
fined under a pressure so far exceeding atmospheric as to 
make the boiling point and the temperature of the fluid 
considerably greater than is observed where water be- 
comes vapor in the open air, is often of such consider- 
able amount as to make its determination a matter of 
real importance. A steam-boiler explosion is but the 
effect of causes which permit the transformation of a 
part of the heat-energy stored in the vessel into mechan- 
ical energy, and the application of that energy to the 
production of results which are often terribly impressive 
and disastrous. The first step, therefore, in any pro- 
posed scheme of study of this important and attractive 
subject is, naturally, an examination of the conditions 
under which energy is stored, and of the magnitude of 
the forces and energies latent in steam and in water 
when confined under high pressure. The first attempt 
to calculate the amount of energy latent in steam, and 
capable of greater or less utilization in expansion by 

*Mainly from a paper by the Author 4< On Steam Boilers as Maga- 
zines of Explosive Energy." Trans. Am. Soc. Mech. Engrs., 1884. 



4 IN TROD UCTION. 

explosion, was made by Mr. George Biddle Airy,* the 
Astronomer Royal of Great Britain, in the year 1863, 
and by the late Professor Rankinet at about the same 
time. 

2. Formulas giving the energy stored in steam and 
in water are now well established. In Rankine's paper, 
just referred to, for example, there were given expres- 
sions for the calculation of the energy and of the ulti- 
mate volumes assumed during the expansion of water 
into steam, as follows, in British and in Metric meas- 
ures: 

TT- 77* {T—2i2 \ T T __ 423.55 (T— IQQ )2. 

T+ 1 1 34.4 T+648 

V== 36.76 (T— 212) . y _ 2.2Q (7^— IOO) 

T+ 1 1 34.4 ' m y+648 • 

These formulas give the energy in foot-pounds and 
kilogrammeters, and the volumes in cubic feet and cubic 
meters. They may be used for temperatures not found 
in the tables to be given, but, in view of the complete- 
ness of the latter, it will probably be seldom necessary 
for the engineer to resort to them. 

The quantity of work and of energy which may be 
liberated by the explosion, or utilized by the expan- 
sion, of a mass of mingled steam and water has been 
shown by Rankine and by Clausius, who determined 
this quantity almost simultaneously, to be easily ex- 

*" Numerical Expression of the Destructive Energy in the Explosions 
of Steam Boilers." Phil. Mag., Nov. 1863. 

f " On the Expansive Energy of Heated Water"; ibid. 



STORED ENERGY OF STEAM. 



5 



pressed in terms of the two temperatures between 
which the expansion takes place. 

When a mass of steam, originally dry, but saturated, 
so expands from an initial absolute temperature, 71, to 
a final absolute temperature, 72, if J is the mechanical 
equivalent of the unit of heat, and i/is the measure, in 
the same units, of the latent heat per unit of weight of 
steam, the total quantity of energy exerted against the 
piston of a non-condensing engine, by unity of weight 
of the expanding mass is, as a maximum, 

O-JT* (£ -l-hyp. lo,.|)+ t J=Rh. . . (A. 

This equation v/as published by Rankine a genera- 
tion ago. # • 

When a mingled mass of steam and water similarly 
expands, if M represents the weight of the total mass 
and m is the weight of the steam alone, the work done 
by such expansion will be measured by the expression, 

U=MJT 2 (^-i- hyp. log. p)+ m ^^H. . .(B) 

This equation was published by Clausius in substan- 
tially this form.f 

It is evident that the latent heat of the quantity m, 
which is represented by mH, becomes zero when the 
mass consists solely of water, and that the first term of 

* Steam Engine and Prime Movers, p. 387. 

f Mechanical Theory of Heat, Browne's Translation, p. 283. 



6 INTRODUCTION. 

the second member of the equation measures the 
amount of energy of heated water which may be set 
free, or converted into mechanical energy, by explosion. 
The available energy of heated water, when explosion 
occurs, is thus easily measurable. 

As has already been stated, this method was first 
applied by Rankine to the determination of the avail- 
able energy of heated water for several selected tem- 
peratures and pressures. It had long been the intention 
of the Author to ascertain the magnitude of the quanti- 
ties of energy residing, in available form, in both steam 
and water, for the whole usual range of temperatures 
and pressures familiar to the engineer, and also to carry 
out the calculations for temperatures and pressures not 
yet attained, except experimentally, but which are 
likely to be reached in the course of time, as the con- 
stantly progressing increase now observable goes on. 
The maximum attainable, in the effort to increase the 
efficiency of the steam engine and in the application of 
steam to new purposes, cannot be to-day predicted, or 
even, so far as the writer can see, imagined. High 
pressures like those adopted by Perkins and by Alban 
may yet be found useful. It was therefore proposed to 
carry out the tables to be constructed far beyond the 
limit of present necessities. 

It was further proposed to ascertain the weights of 
steam and of water contained in each of the more com- 
mon forms of steam boiler, and to determine the total 
and relative amounts of energy confined in each under 
the usual conditions of working in every-day practice, 



FORMULAS FOR ENERGY. 7 

and thus to ascertain their relative destructive power in 
case of explosion. 

At the commencement of this work, the Author em- 
ployed the late Mr. W. G. Cartwright, as compu- 
ter, and, with his aid, prepared tables extending from 
50 pounds per square inch to 100 at intervals of ten 
pounds, up to 250 with intervals of 25 pounds, then 
300, and up to 1000 pounds per square inch by 
100 pounds, and with larger intervals up to 10,000 
and 20,000 pounds. The available energy of the 
heated water was computed, the energy obtain- 
able from the so-called " latent heat," and their 
sum, i. e., the available energy of steam per unit 
of weight. In the course of this work, each figure 
was calculated independently by two computers, and 
thus checked. As a further check, the figures so ob- 
tained were plotted, and the curve representing the law 
of their variation was drawn. This was a smooth curve of 
moderate curvature and an incorrect determination was 
plainly revealed, and easily detected, by falling outside 
the curve. Three curves were thus constructed, which 
will be given later : (1) The Curve of Available Energy 
of Heated Water; (2) The Curve of Available Energy 
of Latent Heat ; (3) the Curve of Available Energy of 
Steam. The second of these curves presents an inter- 
esting peculiarity which will be pointed out when 
studying the forms of the several curves and the tables 
of results. 

The work was interrupted by more pressing duties, 
and was finally resumed in the spring of 1884 and com- 



8 INTRODUCTION. 

pleted in the form now presented. The computers of 
the more complete tables here given were Messrs. 
Ernest H. Foster, and Kenneth Torrance, who, 
pursuing the same method as was originally adopted 
lor the earlier computations, have revised the whole 
work, recalculating every figure, extending the tables 
by interpolation, and carrying them up to a still 
higher pressure than was originally proposed. The 
tables here presented range from 20 pounds per square 
inch, (1.4 kgs. per sq. cm.) up to 100,000 per square 
inch (7,030.83 kgs. per sq. cm.) the maximum probably 
falling far beyond the range of possible application, its 
temperature exceeding that at which the metals retain 
their tenacity, and, in some cases, exceeding their melt- 
ing points. These high figures are not to be taken as 
exact The relation of temperature to pressure is ob- 
tained by the use of Rankine's equation, of which it can 
only be said that it is wonderfully exact throughout the 
range of pressures within which experiment has ex- 
tended, and within which it can be verified. The val- 
ues estimated and tabulated are probably quite exact 
enough for the present purposes of even the military 
engineer and ordnance officer. The form of the equa- 
tion, and of the curve representing the law of variation 
of pressure with temperature, indicates that, if exact at 
the familiar pressures and temperatures, it is not likely 
to be inexact at higher pressures. The curve, at its 
upper extremity becomes nearly rectilinear. 

3. The Calculated Energy of Water and Steam 
are given in the table which follows, and which presents 



CALCULATED ENERGY. 9 

the values of the pressures in pounds per square inch 
above a vacuum, the corresponding reading of the steam- 
gauge (allowing a barometric pressure of 1 4. 7 pounds 
per square inch), and the same pressures reckoned in 
atmospheres, the corresponding temperatures as given by 
the Centigrade and the Fahrenheit thermometers, and 
as reckoned both from the usual and the absolute zeros. 
The amount of the explosive energy of a unit weight of 
water, of the latent heat in a unit weight of steam, and 
the total available heat- energy of the steam, are given 
for each of the stated temperatures and pressures 
throughout the whole range in British measures, atmo- 
spheric pressures being assumed to limit expansion. 
The values of the latent heats are taken from Regnault, 
for moderate pressures, and are calculated for the 
higher pressures, beyond the range of experiment, by 
the use of Rankine's modification of Regnault's formula. 



10 



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4. The Deductions from these calculations are of 
extraordinary importance and interest. Studying the 
table, the most remarkable fact noted at the lower press- 
ures is the enormous difference in the amounts of en- 
ergy, in available form, contained in the water and in 
the steam, and between the energy of sensible heat and 
that of latent heat, the sum of which constitutes the 
total energy of the steam. At 20 pounds per square 
inch above zero (1.36 atmos.), the water contains but 
145.9 foot-pounds per pound; while the latent heat is 
equivalent to 16,872.9 foot-pounds, cr more than 115 
times as much; i. e. f the steam yields 115 times as 
much energy in the form of latent heat, per pound, as 
does the water from which it is formed, at the same tem- 
perature. The temperature is low ; but the amount of 
energy expended in the production of the molecular 
change resulting in the conversion of the water into 
steam is very great, in consequence of the enormous ex- 
pansion then taking place. At 50 pounds, the ratio is 
20 to 1 ; at 100 pounds per square inch, it is 14 to 1, 
at 500 it is 5 to I ; while at 5000 pounds the energy of 
latent heat is but 1.4 that of the sensible heat. The 
two quantities become equal at 7500 pounds. At the 
highest temperature and pressure tabled, the same law 
would make the latent heat negative ; it is of course un- 
certain what is the fact at that point. 

At 50 pounds per square inch the energy of heated 
water is 2550.4 foot-pounds, while that of the steam is 
68,184, or enough to raise its own weight to a height in 
each case of a half-mile or of 12 miles. At 75 pounds 



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ABSOLUTE PRESSURE; POUNDS PER SQUARE INCH. 

Fig. 1 — Curves of Temperature and Latent Heat. 



14 



INTRODUCTION, 



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ABSOLUTE PRESSURE IN POUNDS PER SQ. IN. 



Fig. 2— Curves of Available Energy. 



THE CURVE OF ENERGY. 



x 5 



the figures are 4816 and 90,739, or equivalent to the 
work demanded to raise the unit weight to a height of 
four-fifths, and of about 17 miles, respectively. At 100 
pounds the heights are over one mile for the water, and 
above 20 miles for the steam. The latent heat is not, 
however, all effective. 

5. The Curve of Energy obtained by plotting the 
tabulated figures and determining the form of the curve 
representing the law of variation of each set, are seen in 
the peculiar set of diagrams exhibited in the accom- 
panying engravings. In Figure 1 are seen the curves of 
absolute temperature and of latent heat as varying with 
variation of pressure. They are smooth and beauti- 
fully formed lines, but have no relation to any of the 
familiar curves of the text books on co-ordinate geome- 
try. In Figure 2 are given the curves of available en- 
ergy of the water of latent heat, and of steam. The 
first and third have evident kinship with the two curves 
given in the preceding illustration; but the curve of 
energy of latent heat is of an entirely different kind, 
and is not only peculiar in its variation in radius of 
curvature, but also in the fact of presenting a maximum 
ordinate at an early point in its course. This maximum 
is found at a pressure of about one ton per square inch, 
a pressure easily attainable by the engineer. 

Examining the equations of those curves it is seen 
that they have no relation to the conic sections, and 
that the curve, the peculiarities of which are here noted, 
is symmetrical about one of its abscissas, and that it 
must have, if the expression holds for such pressures, 



1 6 INTRODUCTION. 

another point of contrary flexure at some enormously 
high pressure and temperature. The formula is not, 
however, a "rational " one, and it is by no means cer- 
tain that the curve is of the character indicated; al- 
though it is exceedingly probable that it may be. The 
presence of the characteristic point, should experiment 
finally confirm the deduction here made, will be likely 
to prove interesting, and it may be important ; its dis- 
covery may possibly prove to be useful. 

The curve of energy of steam is simply the curve ob- 
tained by the superposition of one of the preceding 
curves upon the other. It rises rapidly at first, with 
increase of temperature, then gradually rises more 
slowly, turning gracefully to the right, and finally be- 
coming nearly rectilinear. The curve of available 
energy of heated water exhibits similar characteristics ; 
but its curvature is more gradual and more uniform. 



STEAM BOILER EXPLOSIONS. 



6. Steam Boiler Explosions are among the most 
terrible and disastrous of the many kinds of accidents 
the introduction of which has marked the advancement 
of civilization and its material progress.* Introduced 
by Captain Savery at the beginning of the 18th Cen- 
tury, with the first attempts to apply steam-power to use- 
ful purposes, they have increased in frequency and in 
their destructiveness of Hie and property continually, 
with increasing steam -pressures, and the uninterrupted 
growth of these magazines of stored energy, until, 
to-day. the amount of available energy so held in control, 
and liable at times to break loose, is often as much as 
two, or even three, millions of foot-pounds (276,500 to 
414,760 kilogram-meters), and sufficient to raise the 
enclosing vessel 10,000, or even 20,000 feet (3048 to 
6096 m.) into the air, the fluid having a total energy, 
pound for pound, only comparable with that of gun- 
powder. 

♦Portions of this chapter are taken from the notes from which a paper 
by the Author u On Steam Boilers as Magazines of Explosive Energy " 
was prepared. See Trans. Am. Society M. E., 1884 ; and Jour. Frank. 
Inst., Nov., 1884. 

17 



1 8 STEAM BOILER EXPLOSIONS. 

A committee of the British Association, at the session 
of 1869, reporting on this subject, after remarking that 
explosions were occurring still, with their accustomed 
frequency and fatality, go on to say : # 

" Sad as it is when those connected with boilers and 
who gain their livelihood from working them are injured, 
it is even more so when outsiders who have no interest 
in their use, or control over their management, are 
victimized by their explosion, more especially when 
those victims are women and children. Such, however, 
is by no means an infrequent occurrence. In one case, 
a child, asleep in its bed, unconscious of all danger, was 
killed on the spot by a fragment of an exploded boiler 
sent through the roof like a thunderbolt. In a second 
case a young woman working at her needle in an upstairs 
room, in her own dwelling, was struck by a boiler which 
was hurled from its seat and dashed against the window 
at which she sat. The injury was serious — her leg had 
to be amputated, and death shortly after ensued. In a 
third case, just as an infant was making its first essay 
across the kitchen-floor in a collier's cottage, a fragment 
from an exploded boiler came crashing through the roof, 
and striking down the child, killed it on the spot. In a 
fourth case, a woman was standing at her own cottage 
door with an infant in her arms, when one of the bricks 
sent flying through the air by the bursting of a boiler 
struck the little one on the head, and killed it in its 
mother's arms. In a fifth case, a group of boys were 

* London Engineer, Oct. 8, 1869, p. 237. 



STEAM BOILER EXPLOSIONS. 



!9 



sporting in a meadow, when the boiler of a locomotive 
engine, just drawn up at an adjoining station, burst, and 
scattering its fragments among the group, killed one of 
the boys on the spot and injured another." And many 
more such incidents might be related. 

In this and the following article it is proposed to 
present the results of a series of calculations relating to 
the magnitude of the available energy contained in 
masses of steam and of water in steam-boilers. This 
energy has been seen to be measured by the amount of 
work which may be obtained by the gradual reduction 
of the temperature of the mass to that due atmospheric 
pressure by continuous expansion. 

The subject is one which has often attracted the atten- 
tion of both the man of science and the engineer. Its 
importance, both from the standpoint of pure science 
and from that of science applied in engineering and the 
minor arts, is such as would justify the expenditure of 
vastly more time and attention than has ever yet been 
given it. Mr. Airy* and Professor Rankinef published 
papers on this subject in the same number of the Phil- 
osophical Magazine (Nov., 1863), the one dated the 3d 
of September and the other the 5th of October of that 
year. The former had already presented an abstract of 
his work at the meeting of the British Association of 
that year. 

In the first of these papers, it is remarked that " very 

*Numerical Expression of the Destructive Energy in the Explosions 
of Steam Boilers. 

f" On the Expansive Energy of Heated Water. 



20 STEAM BOILER EXPLOSIONS. 

little of the destructive effect of an explosion is due to 
the steam which is confined in the steam-chamber at 
the moment of the explosion. The rupture of the 
boiler is due the expansive power common at the 
moment to the steam and the water, both at a tempera- 
ture higher than the boiling point; but as soon as the 
steam escapes, and thereby diminishes the compressive 
force upon the water, a new issue of steam takes place 
from the water, reducing its temperature; when this 
escapes, and further diminishes the compressive force, 
another issue of steam of lower elastic force from the 
water takes place, again reducing its temperature ; and 
so on, till at length the temperature of the water is 
reduced to the atmospheric boiling point, and the press- 
ure of the steam (or rather the excess of steam-pressure 
over atmospheric pressure) is reduced to o." 

Thus it is shown that it is the enormous quantity of 
steam so produced from the water, during this continu- 
ous but exceedingly rapid operation, that produces the 
destructive effect of steam-boiler explosions. The action 
of the steam which may happen to be present in the 
steam- space at the instant of rupture is considered 
unimportant. 

Mr. Airy had, as early as 1 849, endeavored to deter- 
mine the magnitude of the effect thus capable of being 
produced, but had been unable to do so in consequence 
of deficiency of data. His determinations, as pub- 
lished finally, were made at his request by Professor W. 
H. Miller. The data used are the results of the experi- 
ments of Regnault and of Fa«rbairn and Tate, on the 



ENERGY OE BOILER EXPLOSIONS. 21 

relations of pressure, volume and temperature of steam, 
and of an experiment by Mr. George Biddle, by which 
it was found that a locomotive boiler, at four atmos- 
pheres pressure, discharged one-eighth of its liquid 
contents by the process of continuous evaporization 
above outlined, when, the fire being removed, the press- 
ure was reduced to that of the atmosphere. The 
process of calculation assumes the steam so formed to 
be applied to do work expanding down to the boiling 
point, in the operation. The work so done is compared 
with that of exploding gunpowder, and the conclusion 
finally reached is that " the destructive energy of one 
cubic foot of water, at a temperature which produces 
the pressure of 60 lbs. to the square inch, is equal to 
that of one pound of gunpowder." 

The work of Rankine is more exact and more com- 
plete, as well as of greater practical utility. The 
method adopted is that which has been described, and 
involves the application of the formulas for the trans- 
formation of heat into work which had been ten years 
earlier derived by Rankine and by Clausius, indepen- 
dently. This paper would seem to have been brought 
out by the suggestion made by Airy at the meeting of 
the British Association. Rankine shows that the energy 
developed during this, which is an adiabatic method of 
expansion, depends solely upon the specific heat and 
the temperatures at the beginning and the end of the 
expansion, and has no dependence, in any manner, upon 
any other physical properties of the liquid. He then 
shows how the quantity of energy latent in heated 



22 STEAM BOILER EXPLOSIONS 

water may be calculated, and gives, in illustration, the 
amount so determined for eight temperatures exceeding 
the boiling point. This subject attracted the attention 
of engineers at a very early date. Familiarity with 
the destructive effects of steam-boiler explosions, the 
singular mystery that has been supposed to surround 
their causes, the frequent calls made upon them, in the 
course of professional practice and of their studies, to 
examine the subject and to give advice in matters relat- 
ing to the use of steam, and many other hardly less 
controlling circumstances, invest this matter with an 
extraordinary interest. 

A steam-boiler is a vessel in which is confined a mass 
of water, and of steam, at a high temperature, and at a * 
pressure greatly in excess of that of the surrounding 
atmosphere. The sudden expansion of this mass from 
its initial pressure down to that of the external air, 
occurring against the resistance of its " shell " or other 
masses of matter, may develop a very great amount of 
work by the transformation of its heat into mechanical 
energy, and may cause, as daily occurring accidents 
remind us, an enormous destruction of life and property. 
The enclosed fluid consists, in most cases, of a small 
weight of steam and a great weight of water. In a 
boiler of a once common and still not uncommon 
marine type, the Author found the weight of steam to be 
less than 250 pounds, while the weight of water was 
nearly 40,000 pounds. As will be seen later, under 
such conditions, the quantity of energy stored in the 
water is vastly in excess of that contained in the steam, 



STORED ENERGY. 



23 



notwithstanding the fact that the amount of energy per 
unit of weight of fluid is enormously the greater in the 
steam. A pound of steam, at a pressure of six atmos- 
pheres (88.2 pounds per square inch), above zero of 
pressure, and at its normal temperature, 177C. (3I9°F.), 
has stored in it about 75 British Thermal Units (32 
Calories), or nearly 70,000 foot-pounds of mechanical 
energy per unit of weight, in excess of that which it 
contains after expansion to atmospheric pressure. A 
pound of water accompanying that steam, and at the 
same pressure, has stored within it about one-tenth as 
much available energy. Nevertheless, the disproportion 
of weight of two fluids is so much greater as to make 
the quantity of energy stored in the steam contained in 
the boiler quite insignificant in comparison with that 
contained in the water. These facts are fully illustrated 
by the figures presented. 

7. The Energy Stored in steam boilers is capable of 
very exact computation by the methods already de- 
scribed, and the application of the results there reached 
gives figures that are quite sufficient to account for the 
most violently destructive of all recorded cases of ex- 
plosion. 

A steam-boiler is not only an apparatus by means of 
which the potential energy of chemical affinity is ren- 
dered actual and available, but it is also a storage- 
reservoir, or a magazine, in which a quantity of such 
energy is temporarily held, and this quantity, always 
enormous, is directly proportional to the weight of 
water and of steam which the boiler at the time 
contains. 



$4 STEAM BOILER EXPLOSION'S. 

Comparing the energy of water and of steam in the 
steam-boiler with that of gunpowder,as used in ord- 
nance, it has been found that at high pressures the 
former become possible rivals of the latter. The energy 
of gunpowder is somewhat variable, but it has been 
seen that a cubic foot of heated water, under a pressure 
of 60 or 70 pounds per square inch, has about the same 
energy as one pound of gunpowder. The gunpowder 
exploded has energy sufficient to raise its own weight 
to a height of nearly 50 miles; while the water has 
enough to raise that weight about one-sixtieth that 
height. At a low red heat, water has about 40 times 
this latter amount of energy in a form to be so ex- 
pended. Steam, at 4 atmospheres pressure, yields 
about one-third the energy of an equal weight of gun- 
powder. At 7 atmospheres, it gives as much energy as 
two-fifths of its own weight of powder, and at higher 
pressures its available energy increases very slowly. 

Below are presented the weights of steam and of 
water contained in each of the more common forms of 
steam-boilers, the total and relative amounts of energy 
confined in each under the usual conditions of working 
in every-day practice, and their relative destructive 
power in case of explosion. 

In illustration of the results of application of tne 
computations which have been given, and for the 
purpose of obtaining some idea of the amount of 
destructive energy stored in steam boilers of familiar 
forms, such as the engineer is constantly called upon to 
deal with, and such as the public are coiuinually en- 



STORED ENERGY. 25 

dangered by, the following table has been calculated. 
This table is made up by Mr. C. A. Carr, U. S. N., from 
notes of dimensions of boilers designed by, or managed, 
at various times, by the Author, or in other ways having 
special interest to him. They include nearly all of the 
forms in common use, and are representative of familiar 
and ordinary practice. 

No. 1 is the common, simple, plain cylindrical boiler. 
It is often adopted when the cheapness of fuel or the 
impurity of the water-supply renders it unadvisable to 
use the more complex, though more efficient, kinds. It 
is the cheapest and simplest in form of all the boilers. 
The boiler here taken was designed by the Author many 
years ago for a mill so situated as to make this the best 
form for adoption, and for the reasons above given. It 
is thirty inches in diameter, thirty feet long, and is rated 
at ten H. P., although such a boiler is often forced up 
to double that capacity. The boiler weighs a little over 
a ton, and contains more than twice its weight of water. 
The water, at a temperature corresponding to that of 
steam at 100 pounds pressure per square inch, contains 
over 46,600,000 foot-pounds of available explosive en- 
ergy, while the steam, which has but one-fifth of one 
per cent, of the weight of the water, stores about 
7.00,000 foot-pounds, giving a total of 47,000,000 foot- 
pounds, nearly, or sufficient to raise one pound nearly 
10,000 miles. This is sufficient to throw the boiler 
19,000 feet high, or nearly four miles, and with an ini- 
tial velocity of projection of 1,100 feet per second. 

Comparing this with the succeeding cases, it is seen 



26 STEAM BOILER EXPLOSIONS. 

TOTAL STORED* ENERGY OF STEAM BOILERS. 



Type. 



i Plain Cylinder. . . , 

2 Cornish 

3 Two-flue Cylinder 

4 Plain Tubular 

5 Locomotive 

6 " 

7 " 

8 

9 Scotch Marine 

io 

ii Flue & Return Tubular 

12 

13 Water Tube 

14 " 

15 " 



Area of 



G. S. H. S. 



Sq. Feet. 



15 

36 
20 
30 



15 

32 
50. 
72. 
72 
70 
100 

1 JO 



120 

730 
400 

851.97 
1070 
i35o 
1200 

875 

768 
1119. 
2324 

1755 
2806 
3000 
3000 



Pressure. 


Rated 


Lbs. per 


Power 


Sq. inch. 


H. P. 


100 


10 


30 


60 


150 


35 


75 


60 


125 


525 


125 


650 


125 


600 


125 


425 


75 


300 


75 


35o 


30 


200 


30 


180 


100 


250 


100 


250 


100 


250 



Weight of 



Boiler. 



2500 
16950 

6775 
9500 
19400 
25000 
20565 
14020 

27°45 
37972 
56000 
56000 
34450 
45000 
54000 



Water. 



-Lbs- 

5764 

27471 

6840 

8255 

5260 

6920 

6450 

6330 

11765 

17730 

42845 

48570 

21325 

28115 

13410 



Steam. 



11.325 

3 r .45 

37.04 

20.84 

21.67 

3i. J 9 

25.65 

19.02 

29.8 

47.2 

69.81 

73.07 

35.31 

58.5 

21.64 



TOTAL STORED ENERGY OF STEAM BOILERS.— Continued. 



Type. 



1 Plain Cylinder... 

2 Cornish 

3 Two-flue Cyl'der 

4 Plain Tubular. . . 

5 Locomotive 

6 li 

7 

8 

9 Scotch Marine . . . 
10 

11 Flue&Ret'nTblr 

12 " 

13 Water Tube. . , 
14 
15 



Stored Energy in (available) 



Water. 



Steam. 



Total. 



46, 

57' 

80. 

50. 

52, 

69, 

64, 

64, 

7i. 

107, 

90, 

102, 

172. 

227, 

108, 



,605,200 
,570,750 
,572,050 
,008,790 
,561,075 
,148,790 
,452,270 
,253,160 
272,370 
,408,340 
i53i,490 
628,410 
455,270 
366,000 
346,670 



Foot lbs.- 
676,698 
709,310 

2,377,357 
1,022,731 
1,483,896 
2,136,802 
1,766,447 
1,302,431 
1,462,430 
2,316,392 
1,570,517 
,643,854 
2,108,] 
3,513,830 
3"i377 



47,28i,4. 

58,260,060 
82,949,407 
51,031,521 
54,044,971 
71,284,592 
66,218,717 

65'555. 59i 
72,734,800 
109,724,732 
92,101,987 
104,272,264 
174,563,380 
230,879,830 
109,624,283 



Energy 
per lb. of 



BTr 



Tot 

W't 



-Ft.lbs^ 



18913 

343 1 
12243 
5372 
2786 
2851 
3219 

4677 
2689 
2889 
1644 
1862 
5067 
5130 
2030 



57M 
1314 
6076 
2871 
2189 
2231 
2448 
3213 
1873 
1968 

93 1 

996 
3073 

3i55 



Max. 


Height of 


Project'n. 


BTr 


Tot 


,-Feet.-^ 


18913 


57*4 


343 1 


i3 x 4 


12243 


6076 


5372 


2871 


2786 


2189 


2851 


2231 


3219 


2448 


4677 


3213 


2689 


1873 


2889 


1968 


1644 


931 


1862 


996 


5067 


3073 


5130 


3i55 


2030 


1626 



Initial 

Velocity 



BTr 



Tot. 



Feet per 
Second. 
606 



1 103 

47i 
888 
588 

423 
428 

455 
549 
416 

43i 
325 
346 
57 1 



290 
625 
43° 
375 
379 
397 
455 
348 
356 
245 
253 
445 
575 45o 
361 .323 



* This *' stored " energy is less than that available in the non-condensing engine 
by the amount of the latent heat of external work (/> x —/a) v * 



STORED ENERGY. 27 

that this is the most destructive form of boiler on the 
whole list. Its simplicity and its strength of form make 
it an exceedingly safe boiler, so long as it is kept in 
good order and properly managed ; but, if through 
phenomenal ignorance or recklessness on the part of 
proprietor or attendant, the boiler is exploded, the con- 
sequences are usually exceptionally disastrous. 

No. 2 was a " Cornish " boiler, designed by the 
Author, about i860, and set to be fired under the shell. 
It was 6 feet by 36, and contained a 36-inch flue. The 
shell and flue were both of iron ^-inch in thickness. 
The boiler was tested up to 60 pounds, at which press- 
ure the flue showed some indications of alteration of 
form. It was strengthened by stay-rings, and the boiler 
was worked at 30 pounds. The boiler contained about 
12 tons of water, weighed itself 7^ tons, and the 
volume of steam in its steam space weighed but 3 1 ]/ 2 
pounds. The stored available energies were about 
57,600,000 foot-pounds, and about 700,000 of foot- 
pounds in the water and steam, respectively, a total of 
nearly 60,000,000. This was sufficient to throw the 
boiler to the height of 3,400 feet, or over three-fifths of 
a mile. 

Comparing this with the preceding, it is seen that the 
introduction of the single flue, of half the diameter of 
the boiler, and the reduced pressure, have reduced the 
relative destructive power to but little more than one- 
sixth that of the preceding form. 

No. 3 is a " two-flue " or Lancashire boiler, similar 
in form and in proportions to many in use on the 



2 g STEAM BOILER EXPLOSIONS. 

steamboats plying on our Western rivers, and which 
have acquired a very unenviable reputation by their 
occasional display of energy when carelessly handled. 
That here taken in illustration was designed by the 
Author, 42 inches in diameter, with two 14-inch flues of 
y% iron, and is here taken as working at a pressure, as 
permitted by law, of 150 pounds per square inch. It is 
rated at 35 horse-power, but such a boiler is often 
driven far above this figure. The boiler contains about 
its own weight, 3 tons, of water, and but 37 pounds of 
steam. The stored available energy is 83,000,000 foot- 
pounds, of which the steam contains but a little above 
five per cent. An explosion would uncage sufficient 
energy to throw the boiler nearly 2^ miles high, 
with an initial velocity of 900 feet per second. Both 
this boiler and the plain cylinder are thus seen to have 
a projectile effect only to be compared to that of ord- 
nance. 

No. 4 is the common plain tubular boiler, substan- 
tially as designed by the Author at about the same time 
with those already described. It is a favorite form of 
boiler, and deservedly so, with all makers and users of 
boilers. That here taken is 60 inches in diameter, con- 
taining 66 3-inch tubes, and is 15 feet long. The speci- 
men here chosen has 850 feet of heating and 30 feet of 
grate surface, is rated at 60 horse-power, but is often 
driven up to 75, weighs 9,500 pounds, and contains 
nearly its own weight of water, but only 2 1 pounds of 
steam, when under a pressure of 75 pounds per square 
inch, which is below its safe allowance. It stores 



STORED ENERGY, 



i 9 



51,000,000 foot-pounds of energy, of which but 4 per 
cent, is in the steam, and this is enough to drive the 
boiler just about one mile into the air, with an initial 
velocity of nearly 600 feet per second. The common 
upright tubular boiler may be classed with No. 4. 

Nos. 5-8 are locomotive boilers, of which drawings 
and weights were furnished by the builders. They are 
of different sizes and for both freight and passenger en- 
gines. The powers are probably rated low. They 
range from 15 to 50 square feet in area of grate, and 
from 875 to 1350 square feet of heating surface. In 
weight the range is much less, running from 2^ to a 
little above 3 tons of water, and from 20 to 30 pounds of 
steam, assuming all to carry 125 pounds pressure. The 
boilers are seen to weigh from 2^ to 3 times as much 
as the water. These proportions differ considerably 
from those of the stationary boilers which have been 
already considered. The stored energy averages about 
70,000,000 foot-pounds and the heights and velocities of 
projection not far from 3000 and 500 feet; although, in 
one case, they became nearly one mile, and 550 feet re- 
spectively. The total energy is only exceeded, among 
the stationary boilers, by the two-flued boiler at 150 
pounds pressure. 

Nos. 9 and 10 are marine boilers of the Scotch or 
"drum" form. These boilers have come into use by 
the usual process of selection, with the gradual increase 
of steam pressures occurring during the past generation 
as an accompaniment of the introduction of the com- 
pound engine and high ratios of expansion. The 



30 STEAM BOILER EXPLOSIONS. 

selected examples are designed for use in recent ves- 
sels of the U. S. Navy. The dimensions are obtained 
from the Navy Department, as figured by the Chief 
Draughtsman, Mr. Geo. B. Whiting. The first is that 
designed for the " Nipsic," the second for the " Des- 
patch/' They are of 300 and 350 horse power, and 
contain, respectively, 73,000,000 and 110,000,000 of 
foot-pounds of available energy, or about 3,000 foot- 
pounds per pound of boiler, and sufficient to give a 
height and velocity of projection of 3,000 and above 
400 feet. These boilers are worked at a lower pressure 
than locomotive boilers ; but the pressure is gradually 
and constantly increasing from decade to decade, and 
the amount of explosive energy carried in our modern 
steam-vessels is thus seen to be already equal to that of 
our locomotives, and in some cases already considerably 
exceeds that which they would carry were they sup- 
plied with boilers of the locomotive type and worked at 
locomotive pressures. The explosion of the locomo- 
tive boiler endangers comparatively few lives and sel- 
dom does serious injury to property, outside the engine 
itself. The explosion of one of these marine boilers 
while at sea would be likely to be destructive of many 
lives, if not of the vessel itself and all on board. 

Nos. 11 and 12 are boilers of the old types, sud^ as 
are still to be seen in steamboats plying upon the hud- 
son and other of our rivers, and in New York harbor 
and bay. No. 1 1 is a return tubular boiler having a 
shell ten feet in diameter by 23 feet long, 2 furnaces 
each 7^ feet deep, 5 15 -inch and 2 9-inch flues, and 85 



STORED ENERGY. 



H 



return tubes, 4 *^ inches by 1 5 feet. The boiler weighs 
25 tons, contains nearly 20 tons of water and 70 pounds 
of steam, and at 30 pounds pressure stores 92,000,000 
foot-pounds of available energy, of which 2^ per cent, 
resides in the steam. This is enough to hoist the boiler 
one- third of a mile with a velocity of projection of 330 
feet per second. The second of these two boilers is of 
the same weight, also of about 200 horse power, but 
carries a little more water and steam, and stores 104,000,- 
000 foot-pounds of energy, or enough to raise it 1,900 
feet. This was a return-flue boiler, 33 feet long and 
having a shell 8^ feet in diameter, flues S}4 to 15 
inches in diameter, according to location. 

The " sectional " boilers are here seen to have, for 
250 horse-power each, weights ranging from about 
35,000 to 55,000 pounds, to contain from 15,000 to 
30,000 pounds of water and from 25 to 58 pounds of 
steam, to store from 110,000,000 to 230,000,000 foot- 
pounds of energy, equal to from 2,000 to 5,000 foot- 
pounds per pound of boiler. The stored available en- 
ergy is thus usually less than that of any of the other 
stationary boilers, and not very far from the amount 
stored, pound for pound, by the plain tubular boiler, 
the best of the older forms. It is evident that their ad- 
mitted safety from destructive explosion does not come 
from this relation, however, but from the division of 
the contents into small portions, and especially from 
those details of construction which make it tolerably 
certain that any rupture shall be local. A violent ex- 
plosion can only come of the general disruption of a 



32 



STEAM BOILER EXPLOSIONS. 



boiler and the liberation at once of large masses of 
steam and water. 

8. The Energy of Steam Alone, as stored in the 
boiler, is given by column 10 of the preceding table. 
It has been seen that it forms but a small and unim- 
portant fraction of the total stored energy of the boiler. 
The next table exhibits the effect of this portion of the 
total energy, if considered as acting alone. 

STORED ENERGY IN THE STEAM SPACE OF BOILERS. 



Type. 



Plain Cylinder 

Cornish 

Two-flue Cylinder. .. 

Plain tubular 

Locomotive 

Scotch Marine 

Flue and Return Tube 
Water-tube 



Energy, 
Total. 



676,693 
709,310 

2,377,357 
1,022,731 
1,483,896 
2,135,802 
1,766,447 
1,302,431 
1,462,430 
2,316,392 

i,57°i5i7 
1,643,854 
2,108,110 
3,513.830 
I ,3 II ,377 



Stored in Steam 




(ft. lbs.) 


Height of 


per lb. of Boiler. 


Projection 


271 


271 ft. 


42 


42 * l 


35i 


35i " 


108 


108 '* 


76 


76 « 


85 


85 " 


86 


86 " 


107 


107 " 


54 


54 ' 


61 


61 " 


28 


28 " 


29 


29 •' 


61 


61 " 


79 


79 " 


24 


24 " 



Initial 
Velocity. 
per sec. 



132 ft. 
3 2 !! 



69 " 
74 

74 * 

83 " 

59 ,: 
62 " 

42 U 

43 

59 

71 '! 
39 



The study of this table is exceedingly interesting, if 
made with comparison of the figures already given, and 
with the facts stated above. It is seen that the height 
of projection, by the action of steam alone, under the 
most favorable circumstances, is not only small, insig- 
nificant indeed, in comparison with the height due the 
total stored energy of the boiler, but is probably en- 
tirely too small to account for the terrific results of ex- 



THE ENERGY OF STEAM ALONE. 



33 



plosions frequently taking place. The figures are those 
for the stored energy of steam in the working boiler ; 
they may be doubled, or even trebled, for cases of low 
water ; they still remain, however, comparatively insig- 
nificant. 

The enormous force of molecular power, even when 
heat is not added to reinforce them, is illustrated by 
the often described experiments of an artillery officer at 
Quebec* and others, in which a large bombshell is filled 









^~- 








~~- "~^- 


*s -\ 


^ 


i 


■*■ 


— -~N 


* .— ^ 






c 


r 

u 


/ 


^■r*£3&W 


> ( 


=EE=^ 


WSk 


Iflll 


|!gf===-' 




"\-^ 


Si^i^B 


iiiPiSlllS 


=Ife 


-=- = 


' = rEr-^E==^ 


^^^i 


iS^s 


53^5====^ 


L-=^=^:-==E 


=5^=^ 



Fig. i. Expansive Force of Ice. 

with water, tightly plugged, and exposed to low temper- 
atures. In such cases the expansive force exerted, 
when freezing, by the formation of ice and the increase 
of volume accompanying the formation of the crystals, 
either drives out the plug, sometimes projecting it 
hundreds of yards (Fig. 3), or actually bursts the thick 
iron case. 

In the more familiar cases of purposely produced 
explosion, the expansion is caused by the production ol 
great quantities of gas previously in solid form. The 



* Phenomena of Hunt : Cazin. 



34 



STEAM BOILER EXPLOSIONS. 



violence of the familiar explosives as used in ordnance, 
in mining operations, is commonly due to this combined 
effect of heat and chemical action, occurring by the 
sudden action of powerful forces. In the steam-boiler 
explosion, mighty forces previously long held in subjec- 
tion, finally overcome all resistance, and their sudden 
application to external bodies constitute the disaster. 

9. Explosion and Bursting are terms which, as 
often technically used by the engineer, represent radi- 







Fig. 4. — An Explosion. 



cally different phenomena. The explosion of a steam- 
boiler is sudden and violent disruption, permitting the 
stored heat-energy of the enclosed water and steam to 
be expended in the enormously rapid expansion of its 
own mass, and, often, in the projection of parts of the 
boiler in various directions with such tremendous power 
as to cause as great destruction of life and property as if 
the explosion were that of a powder-magazine. The 



EXPLOSION AND BURSTING. 35 

bursting of a boiler is commonly taken to be the rup- 
ture, locally, of the structure, by the yielding of its 
weakest part to a pressure which, at the moment, may 
not be deemed excessive, but which is too great for the 
weakened spot. The collapse of a flue is a form of 
rupture which is ordinarily considered as of the second 
class. With high steam-pressure, the bursting, or the 
collapse, of a flue, may occur with a loud report, and 
may even cause some displacement of the boiler ; but it 
is not generally termed an explosion where the boiler is 
simply upturned and is not torn into separated pieces. 
There is, however, no real boundary, and the one 
grades into the other, with no defined line of demarka- 
tion. 

It occasionally happens that an explosion takes place 
with such extraordinary violence and destructive effect 
that it has been thought best, especially by French 
writers, to class it by itself, and it is denoted a detonant 
or fulminant explosion, "explosion fulminante" In 
such cases, the report is like that of an enormous piece 
of ordnance ; the boiler is often rent into many parts, 
or even completely broken up as if by dynamite ; and 
surrounding objects are destroyed as if by the discharge 
of a park of artillery. 

In any steam-boiler, there may, at any time, exist a 
state of equilibrium between the resisting power of the 
boiler and the steam-pressure. In ordinary working, 
the latter is far within the former, but as time passes, 
the limiting condition is gradually approached, and, in 
every explosion, the line is passed. The pressure may 



36 STEAM-BOILER EXPLOSIONS. 

rise until the limit of strength is attained ; or the resist- 
ing power of the boiler may decrease to the limit ; in 
either case, the passage of the line is marked by explo- 
sion or a less serious method of yielding. 

io. The Causes of Boiler Explosions are numer- 
ous, but are usually perfectly well understood. Where 
uncertainty exists, it is probably the fact that, were the 
cause ascertained, it would be found to be simple and 
well known. It is, nevertheless, true that some author- 
ities, including a few experienced and distinguished 
members of the engineering profession, believe that 
there are causes, at once obscure and of great potency and 
energy, which are not yet satisfactorily understood. In 
this work, the many causes to which explosions are, by 
various practitioners and writers, attributed, may be 
divided into the known, the probable, the possible, the 
improbable, and the impossible and absurd. 

To the first class belong the general and fairly uniform 
weakness of boilers as compared with the steam-press- 
ure carried ; the sticking of safety valves, and the thou- 
sand and one other causes having their origin in the 
ignorance, the carelessness, or the utter recklessness of 
the designer, the builder, or the attendants entrusted 
with their management. To this class may be assigned 
the causes of by far the greater proportion of all explo- 
sions; and the Author has sometimes questioned whether 
this category may not cover absolutely all such catastro- 
phes. To the second class may be assigned "low 
water," a cause to which it was once customary to attri- 
bute nearly all explosions, but which is known to be 



THE CAUSES OF BOILER EXPLOSIONS. 



37 



seldom operative, and so seldom that some authorities 
now question the possibility of its action at all.* Among 
the possible causes, acting rarely and under peculiar 
conditions, the Author would place the overheating of 
water, and the storage of energy in excess of that in 
the liquid at the temperature due the existing pressure ; 
the too sudden opening of the throttle-valve, or the 
safety-valve, producing primingand shock; the spheroidal 
state of water; and perhaps other phenomena. The 
improbable include the latter, however. The action of 
electricity, a favorite idea with the uninformed, may be 
taken as an example of the impossible and absurd. 
The actual causes of a vast majority of boiler explosions 
are now determined by skilled engineers, inspectors and 
insurance experts; and it is by them generally supposed 
that no so-called " mysterious " causes exist, in the 
sense that they are phenomena beyond the present 
range of human knowledge and scientific investigation. 

All recent authorities agree in attributing boiler-ex- 
plosions, almost without exception, to one or another of 
the following general classes of causes, and the Author 
is inclined to make no exception : 

(i.) Defective design : resulting in weakness of shell, 
of flues, or of bracing or staying; in defective circula- 
tion; faulty arrangement of parts; inefficiency of pro- 
vision for supplying water or taking off steam ; and de- 
fects in arrangement leading to strains by unequal ex- 

* See opinion of Mr. J. M. Allen, Sibley College Lecture, Sci. Am. 
Supplement, Feb. 19, 1887, p. 9272. 






$8 STEAM BOILER EXPLOSIONS. 

pansion, and other matters over which the designer 
had control, 

(2.) Malconstruction: including choice of defective 
or improper material ; faulty workmanship ; failure to 
follow instructions and drawings ; omissions of stays or 
braces. 

(3.) Decay of the structure with time or in conse- 
quence of lack of care in its preservation; local defects 
due to the same cause or to some unobserved, or con- 
cealed leakage while in operation. 

(4.) Mismanagement in operation, giving rise to ex- 
cessive pressure ; low water ; or the sudden throwing 
of feed-water on overheated surfaces ; or the produc- 
tion of other dangerous conditions ; or failure to make 
sufficiently frequent inspection and test, and thus to 
keep watch of those defects which grow dangerous 
with time. 

Weakness of boiler or over-pressure of steam are the 
usual immediate causes of explosions. 

It has often been suggested that the most destructive 
boiler-explosions may be attributable to electricity and 
may illustrate the effect of an unfamiliar form of light- 
ning. Such hypotheses are, however, absurd. No stor- 
age and concentration of electricity could' be produced 
in a vessel composed of the best of conducting ma- 
terials and inclosing a mass of fluid incapable of causing 
electrical currents, either great or small, under the con N 
ditions observed in the steam-boiler. The production 
of electricity, seen in Armstrong's experiments, a phe^ 
nomenon sometimes thought to support this theory, is 



THE CAUSES OF BOILER EXPLOSIONS. 39 

simply the result of the friction of a moving jet of 
steam on the nozzle from which it issued, and presents 
not the slightest reason for supposing that the elec- 
trical hypothesis of the origin of boiler-explosions have 
any basis of fact. 

Professor Faraday, in a report to the British Board of 
Trade, May, 1859, states his belief in the absurdity of 
the idea that the water within a steam-boiler may be- 
come decomposed and the explosion of a mixture of 
gasses so produced may burst a boiler. # * * * " As 
respects the decomposition of the steam by the heated 
iron, and the separation of hydrogen, no new danger is 
incurred. Under extreme circumstances, the hydrogen 
which could be evolved would be very small in quantity, 
would not exert greater expansive force than the steam, 
and would not be able to burn with explosion, and 
probably not at all if it met the steam, escaping through 
an aperture into the air, or even into the fireplace." 

Decomposition cannot occur in the steam-boiler, or- 
dinarily, and if it were to happen in consequence of 
low water and overheated plates, no oxygen could re- 
main free to explosively combine with it. 

A half century ago, M. Arago, in writing of steam 
boiler explosions,* asserted " that no cause of explosion 
exists which cannot be avoided by means at once sim- 
ple and within reach of every one." A committee of the 
Franklin Institute, in 1830, asserted t of boiler-explo- 

* Mem. Roy. Acad. Sci., Inst. France ; xxi. 
t Journal Franklin Institute, 1830. 



4° 



STEAM BOILER EXPLOSIONS. 



sions that " they proceed, in most cases, from defective 
machinery, improper arrangement or distribution of 
parts, or finally, from carelessness in management." 
These conclusions are fully justified by all later experi- 
ence, and it is now admitted by all accepted authorities 
that a careful examination and study of the facts of the 
case will almost invariably enable the experienced en- 
gineer to determine the origin of the disaster. It fol- 
lows that it is perfectly practicable to so design, con- 
struct, and manage steam- boilers that there shall be ab- 
solutely no danger of explosion. 

That the great majority, if not all, explosions are due 
to preventible causes was thus very early recognized. 
President Andrew Jackson, in his fifth Annual Message 
3?/ to Congress, Dec. 3d, 18,83, says: 

" The many distressing accidents which have of late 
occurred in that portion of our navigation carried on by 
the use of steam-power, deserves the immediate and un- 
remitting attention of the constituted authorities of the 
country. The fact that the number of those fatal dis- 
asters is constantly increasing, notwithstanding the great 
improvements which are everywhere made in the ma- 
chinery employed, and the rapid advances which have 
been made in that branch of science, show very clearly 
that they are in a great degree the result of criminal 
negligence on the part of those to whose care and at- 
tention the lives and property of our citizens are so ex- 
tensively entrusted. 

"That these evils may be greatly lessened, if not sub- 
stantially removed, by means of precautionary and penal 






THE CAUSES OF BOILER EXPLOSIONS. 41 

legislation, seems to be highly probable ; so far, there- 
fore, as the subject can be regarded as within the con- 
stitutional purview of Congress, I earnestly recommend 
it to your prompt and serious attention.' ' 

Modern experience and recent investigation confirm 
these statements. 

The United Society of Boiler-makers express the 
general opinion of engineers on this subject in the follow- 
ing language : # 

" If masters who manufacture boilers and those who 
use them would be more judicious in their selection of 
boilers made of the best materials and after the most 
approved principles, we should rarely listen to the hor- 
rifying details of boiler explosions." 

11. The Statistics of Explosions have been very 
carefully collected for many years in some European 
communities, notably in France, and are now given for 
the United States in very reliable form by inspectors, 
governmental and private, who are thoroughly familiar 
with the subject. The following is a list reported for 
the year 1885 

* London Engineer, July 29, 1870, p. 77. 



4 2 



STEAM BOILER EXPLOSIONS. 
CLASSIFIED LIST OF BOILER EXPLOSIONS. 






Saw-mills and wood-working shops 

Locomotives 

Steamboats, tugs, etc 

Portables, hoisters and agricultural engines. . . 

Mines, oil wells, collieries, etc 

Paper-mills, bleachers, digesters, etc 

Rolling-mills and iron-works 

Distilleries, breweries, sugar-houses, dye-houses, 

rendering establishments, etc 

Flour-mills and elevators 

Textile manufactories 

Miscellaneous 



Total per month « ' 14 20 14 7 

Persons killed, total 220 per month '242220 9 

Persons injured, total 288 per month.. 35,3028 9 



32 



19 
13 40 



33 



18 



18 



155 



Boilers used in saw-mills are most frequently ex- 
ploded, presumably because of the cheapness of their 
construction, and the unskillfulness exhibited in their 
management; boilers in mines are next in number of 
casualities. Factory-boilers explode with comparative in- 
frequency. In the United States, according to the best 
estimates which the Author has been able to make, 
about one boiler in 10,000 explodes among those which 
are regularly inspected and insured, and ten times that 
proportion among uninspected and uninsured boilers. 



THE STA TISTICS OF EXPLOSIONS 



43 



According to Reiche,* in Great Britain, recently, one 
explosion has occurred in every 500 boilers not under 
inspection ; in Prussia, one in 1,000 under state control 
and inspection; and in Great Britain one in 10,000 
boilers in charge of the private inspection companies. 
Explosions might become almost unknown were a 
proper system of inspection and compulsory repair in- 
troduced. 

In Great Britain the proportion of explosions is 
much less than in the United States, the average num- 
ber being less than one-twentieth of one per cent, and 
the loss of life about three to every two explosions. In 
Great Britain, as in the United States and elsewhere, 
the majority of explosions are due to negligence. 

The returns of boiler-explosions in Great Britain and 
the United States show that not only in number but in 
destructiveness the record of the United States always 
exceeds that of Great Britain, as is seen in the following 
table. 





No. Explosions. 


No. 


Fatalities. 


No. Persons injd. 




1884. 


1885. 


1884. 


1885. 


1884. 


1885. 


Great Britain 


36 
152 


43 
155 


24 

254 


40 
220 


49 
261 


62 


United States 


288 



' Anlage und Betrieb der Dampfkessel ; H. v. Reiche ; Leipzig, 



1876. 



44 



STEAM BOILER EXPLOSIONS. 





No. Explosions per Million 
Inhabitants. 


No. Fatalities per Explosion. 




1884. 


1885. 


1884. 


1885. 


Great Britain 

United States 


1 
3 


1.17 
3 °9 


.e 7 
1.67 


.93 
1.42 



The causes of the 43 explosions in Great Britain are 
reported to have been : 

Cases. 

Deterioration or corrosion of boilers and safety-valves . . 20 

Defective design or construction of boiler or fittings. . . . 11 

Shortness of water. a , . t , 4 

Ignorance or neglect of attendants, . . , t . . . 4 

Miscellaneous , c 4 

Total e 43 



For the United States there are estimated to have 
been dangerous cases, classified thus : 



Causes. 

Deterioration or corrosion of boilers and safety 
valves 

Defective design or construction of boiler or 
fittings 

Shortness of water 

Ignorance or neglect of attendants ....... 

Miscellaneous ......... . , . . . , 



Whole No 



17,873 

15,895 

130 

6,404 

6,928 



Dangerous. 



1,727 

2,957 

56 

983 

1,403 



THE STATISTICS OF EXPLOSIONS. 



45 



The following are two classified lists of defects and 
causes of dangerous conditions, where, in one case, over 
6,000 boilers, and in the other above 4,000 were 
inspected in one month :* 



Nature of Defects. 



Deposit of sediment 

Incrustation and scale 

Internal grooving . 

Internal corrosion 

External corrosion 

Broken, loose, and defective braces and stays, 

Defective settings. 

Furnaces out of shape 

Fractured plates 

Burned plates 

Blistered plates 

Cases of defective riveting 

Defective heads 

Leakage around tube ends 

Leakage at seams 

Defective water guages 

Defective blow-offs 

Cases of deficiency of water 

Safety-valves overloaded 

Safety-valves defective in construction 

Defective pressure-guages 

Boilers without pressure-guages 

Defective hand-hole plates 

Defective hangers 

Defective fusible plugs 

Total 



Whole Number. Dangerous, 



458 


32 


630 


55 


20 


7 


155 


16 


346 


23 


205 


39 


178 


17 


248 


12 


123 


65 


89 


22 


254 


11 


1,649 


187 


30 


15 


974 


33i 


574 


22 


163 


27 


30 


8 


5 


2 


29 


7 


42 


7 


238 


19 


4 





3 


3 


13 





1 






6.453 



927 



* " The Locomotive," Dec, 1884 ; Sept., 1886. 



4 6 



STEAM BOILER EXPLOSIONS. 



Nature of Defects. 



Cases of deposit of sediment 

Cases of incrustation and scale 

Cases of internal grooving 

Cases of internal corrosion 

Cases of external corrosion 

Broken and loose braces and stays 

Settings defective 

Furnaces out of shape 

Fractured plates 

Burned plates 

Blistered plates 

Cases of defective riveting 

Defective heads 

Serious leakage around tube ends 

Serious leakage at seams 

Defective water gauges 

Defective blow-offs 

Cases of deficiency of water 

Safety-valves overloaded 

Safety-valves defective in construction. 

Pressure-guages defective 

Boilers without pressure-gauges 



Total , 



Whole Number. 



5i6 

781 
28 
173 
323 
50 
248 
179 
108 
100 
257 
459 
36 
461 
205 
161 

43 
18 

25 
21 

215 
2 

4,409 



Dangerous. 



45 

54 

4 

10 

28 
13 
17 
14 
45 
25 
21 

49 
17 
26 

27 
8 
8 
6 
6 
6 

26 
2 

457 



It is seen that many of these defects, all of which are 
dangerous and liable to cause explosion, are of very 
variable frequency, as, for example, defective riveting, 
which is more tha^n twice as common, in the first list, as 
any other defect, but which stands number three in the 
second ; while other defects are of quite regular occur- 
rence, as the presence of sediment and of scale, groov- 
ing, and other corrosion, injured plates and defective 
guages. Sediment, oxidation, and defective workman- 
ship are evidently the most prolific causes of danger ; 
and unequal expansion, to which many of the reported 
cases of leakage are attributable, hardly less so. 



THEORIES AND METHODS. 47 

An inspection of these tables plainly shows that the 
causes of steam-boiler explosions are commonly perfectly 
simple and are well understood ; and a person familiar 
with the subject usually wonders that explosions occur 
as infrequently as they do, where there are so many 
sources of danger and where so little intelligence and 
care is exhibited in their design, construction, and 
operation. There are, however, some interesting phe- 
nomena, and some very ingenious theories as to method 
of liberation of the enormous stock of energy of which 
every boiler is a reservoir, to which attention may well 
be given. 

12. Theories and Methods of explosions due to 
other causes than simple increase of steam-pressure or 
decrease in strength of boiler, and of such accidents as 
are common and well understood, and produce the 
greater number of disasters of the class here studied, 
are as various as they are interesting. The vast ma- 
jority of all boiler-explosions have been, as has been 
seen, found to be due to causes which are readily de- 
tected and are the simplest and most obvious possible. 
Here and there, however, an explosion takes place 
which is so exceptionally violent, or which occurs under 
such unusual and singular conditions, as to give rise to 
question whether some peculiar phenomenon is not con- 
cerned in bringing about so extraordinary a result. 
Nearly all explosions have been produced either by a 
gradual rise in pressure until the resisting power of the 
boiler has been exceeded and an extended rupture lib- 
erates the stored energy; or by a gradual reduction 



4 8 STEAM BOILER EXPLOSIONS. 

of the strength of the structure until, at last, it is insuf- 
ficient to withstand the ordinary working pressure, and 
a general yielding leads to the same result. Such cases 
require little comment and no explanation. But the 
rare instances in which a sudden development of forces 
far in excess of those exhibited in regular working 
have been believed to have been observed, have given 
rise to much speculation, to many ingenious theories, 
and to an immense amount of speculation and miscon- 
ception on the part of those who are unfamiliar with 
science and without experience in the operation of this 
class of apparatus. 

Explosions probably always occur from perfectly 
simple and easily comprehended causes, are always the 
result of either ignorance or carelessness, and are 
always preventible where intelligence and conscientious- 
ness govern the design, the construction, and the man- 
agement of the boiler. A well-designed boiler, properly 
proportioned for its work and to carry the working 
pressure, well built, of good materials, and intelligently 
and carefully handled, has probably never been known 
to explode. Explosions probably rarely occur, with 
either a gradually increasing pressure of steam, or 
decreasing strength of boiler unless the strength of the 
structure is quite uniform ; local weakness is a safety- 
valve which permits a " burst" and insures against that 
more general disruption which is called an " explosion." 
A long line of weakened seam, an extended crack, or a 
considerable area of surface thinned by corrosion may 
lead to an explosion and a general breaking up of the 



THEORIES AND METHODS. 



49 



whole apparatus ; but any minor defect, when its site is 
surrounded by strong parts, will not be likely to pro- 
duce that result. 

The Method of Explosion is, in the great major- 
ity of cases, the opening of a small orifice at a point of 
minimum strength, with outrush of water or steam, or 
both, the rapid extending of the rupture until it becomes 
so great and the operation so rapid that, no time being 
given for the gradual discharge of the enclosed fluids, 
the boiler is torn violently apart by the internal unre- 
lieved pressure and distributed in pieces, the number of 
which is determined by the character and extent of the 
lines or areas of weakness. The violence of the pro- 
jection of the detached parts depends on the magnitude 
of the pressure and the rapidity with which disruption 
takes place. The most destructive explosions are often 
distinguished by a general breaking up of the whole 
structure. In the case of the " burst " boiler, the 
opening is of limited extent and the contents of the 
boiler are discharged without tearing it in pieces. 

" Colburn's Theory," to be presently described, is an 
attempt to state the method of explosion and the reasons 
therefor, and the other theories, accepted or otherwise, 
usually attempt the same thing for general or special 
cases. 

13. Clark and Colburn's Theory of boiler-explo- 
sions has been accepted as a " working hypothesis " by 
many engineers and has some apparent foundation in 
experimentally ascertained fact. This theory is attri- 



rjo STEAM BOILER EXPLOSIONS. 

buted to Mr. Zerah Colburn,* but was probably, as 
stated by Mr. Colburn himself, original with Mr. D. K. 
Clark, who suggests that a rupture initiated at the 
weakest part of a boiler, above or near the water-line, 
may be extended and an explosion precipitated by the 
impact of a mass of water carried toward it by the 
sudden outrush of a quantity of steam, precisely as the 
" water-hammer " observed so frequently in steam- 
pipes causes an occasional rupture of even a sound and 
strong pipe. In fact, many instances have been observed 
in which the rent thus presumed to have been produced 
has extended not only along lines of reduced section, 
but through solid iron of full thickness and of the best 
quality. It is thus that Mr. Clark would account for 
the shattering and the deformation of portions of the 
disrupted boiler which are often the most striking and 
remarkable phenomena seen in such instances. 

Colburn suggests that the explosion, in such cases, 
although seemingly instantaneous, may actually be a 
succession of operations, three or four, at least, as the 
following: 

(i.) The initial rupture under a pressure which may 
be, and probably often is, the regular working pressure; 
or it may be an accidentally produced higher pressure ; 
the break taking place in or so near the steam-space that 
an immediate and extremely rapid discharge of steam 
and water may occur. 

*Steam Boiler Explosions : Zerah Colburn. London: John Weale. 
i860. 



CLARK AND COLB URN'S THEORY. 51 

(2.) A consequent reduction of pressure in the 
boiler, and so rapid that it may become considerable 
before the inertia of the mass of water will permit its 
movement. 

(3.) The sudden formation of steam in great quan- 
tity within the water and the precipitation of heavy 
masses of water, with this steam, toward the opening, 
impinging upon adjacent parts of the boiler and break- 
ing it open, causing large openings or extended rents, 
and, often, shattering the whole structure into numerous 
pieces. 

(4.) The completion of the vaporization of the now 
liberated mass of water to such extent as the reduction 
of the temperature may permit, and the expansion of 
the steam so formed, projecting the detached parts to 
distance depending on the extent and velocity of this 
action. 

This series of phenomena may evidently be the 
accompaniment of any explosion, to whatever cause the 
initial rupture may be due. One circumstance lending 
probability to this theory is the rarity of explosions 
originating in the failure of " water-legs " or other parts 
situated far below the water-line. This occasionally hap- 
pens, as was seen some time ago at Pittsburgh, in the 
explosion of a vertical boiler, caused by a crack in the 
water-leg; but it is almost invariably observed that 
explosions occur where long lines of weakened metal, 
defective seams, or of " grooving " extend nearly or 



52 STEAM BOILER EXPLOSIONS, 

quite to the steam space.* A local defect well below 
the water-line would usually simply act as a safety-valve, 
discharging the contents of the boiler without explosion. 

14. Corroboratory Evidence has been here and there 
found. Lawson's experiments, and those of others, as 
well as many accidental explosions, have supplied evi- 
dence somewhat, but not absolutely, corroboratory of 
the Clark and Colburn theory. Mr. D. T. Lawson, hav- 
ing become convinced of the truth of the Clark and 
Colburn theory, further conceived the idea that the 
opening and sudden closing of the throttle or the safety- 
valve might cause precisely the same succession of 
phenomena, and lead to the explosion of boilers ; the 
opening starting the current, and the closing of the valve 
producing impact that may disrupt the boiler. To test 
the truth of his hypothesis, he made a number of experi- 
ments, and succeeded in exploding a new and strong 
boiler at a pressure far below that which it had immedi- 
ately before safely borne. As a preventive, he proposed 
the introduction of a perforated sheet-iron diaphragm, 
dividing the interior of the boiler at or near the water- 
line, the expectation being that it would check the 
action described by Colburn and prevent that percussive 
effect to which explosion was attributed by him, and 
also that it would be found to possess some other advan- 
tages. 

The experiments were made at Munhall, near Pitts- 

* The "Westfield" explosion illustrates this case. Jour. Frank. Inst., 

1875. 



CORROBORA TOR Y E VIDENCE. 5 3 

burgh, Pa., in March, 1882, the boiler being of the 
cylindrical variety, 30 inches (76 cm.) in diameter and 
7^ feet (2.06 m.) in length, of iron 3- 16 inch (0.48 cm.) 
in thickness. Its strength was estimated at 430 pounds 
per square inch (28^3 atmos.) It was fitted with a dia- 
phragm, as above described. 

After some preliminary tests, the following were made,* 
the valve being opened at intervals and suddenly closed 
again at the pressures given below, as taken from the 
log. A steam- guage was attached to the boiler above 
and another below the diaphragm. The boiler contained 
18 inches of water. Steam was generated slowly, and 
when the pressure had reached 50 pounds, operating 
the discharge valve began, with the following results : 

* Report of U.S. Inspectors to the Secretary of the Treasury, Men, 
23d 1882. 



54 



STEAM BOILER EXPLOSIONS. 



Steam pressure 
at which dis- 


Steam-gauge above 
diaphragm. 


Steam-gauge below the 
diaphragm. 


charge valve was 
raised. 


Needle fell 
below. 


Needle rose 
above. 


Needle fell 
below. 


Needle rose 
above 


Lbs. 


Lbs. 


Lbs. 


Lbs. 


Lbs. 


50 


7 


3 


3 


00 


80 


10 


7 


4 


00 


100 


12 


7 


5 


3 


125 


15 


15 


8 


4 


150 


20 


20 


8 


7 


175 


15 


23 


10 


10 


200 


20 


20 


15 


00 


225 


30 


20 


12 


00 


230 


40 


30 


10 


00 


250 


25 


20 


10 


00 


275 


30 


25 


15 


00 


300 


40 


35 


15 


00 



When the pressure in the boiler reached 300 pounds 
to the square inch, it was decided that the boiler had 
been sufficiently tested, and the boiler was emptied and 
inspected. The rivets, seams, and all the other parts of 
the boiler were examined, and no strain, rupture, or 
weakness was discovered. The diaphragm was then cut 
out, leaving the flanges riveted to the sides of the shell 
and across the heads. The boiler was then again tested, 
with the following results ; 



CORROBORA TOR Y E VIDENCE. 



55 



Steam pressure 


Steam-guage attached to the 
boiler in the steam-space. 


Steam-guage attached to the 
boiler in water-space. 


at which dis- 

cha !ge valve was 

raised. 






Needle fell 
below. 


Needle rose 
above. 


Needle fell 
below. 


Needle rose 
above. 


Lbs. 


Lbs. 


Lbs. 


Lbs. 


Lbs. 


IOO 


3 


00 


3 


00 


125 


2 


00 


3 


00 


150 


5 


00 


5 


00 


175 


4 


2 


3 


2 


200 


5 


00 


5 


00 


210 


3 


00 


3 


00 


225 


5 


00 


3 


00 


235 


Exploded. 









When the discharge- valve was opened at 235 pounds 
pressure, it caused the explosion of the boiler; it was 
blown into fragments. The iron was torn and twisted 
into every conceivable shape ; strips of various sizes and 
proportions were found in all directions. The boiler 
did not always tear at the seams, but principally in the 
solid parts of the iron. 

At the time of the explosion the water-line was 
higher than during the test immediately preceding. 
At an earlier privately made experiment, as reported 
by the same investigator, an explosion of a new boiler 
had been similarly produced at one-half the pressure 
which it had been estimated that the boiler might sus- 
tain. A significant fact exhibited in the record is the 
enormously greater fluctuation of pressure in the boiler 



5 6 STEAM BOILER EXPLOSIONS. 

during the first than during the second trial, and the 
difference in the amount of that fluctuation above and 
below the diaphragm. 

The result of this action in the ordinary operation of 
the safety-valve or of the throttle-valve is apparently 
extremely uncertain. Many explosions have occurred 
under such circumstances as would seem to indicate the 
probability of the action described having been their 
cause, the disaster following the opening of safety 
valve, or of the throttle at starting the engines. 

On the other hand, these operations are of constant 
occurrence and with weak and dangerous boilers, and 
such explosions are, nevertheless, extremely rare. The 
Author, while officially engaged in attempting the experi- 
mental production of boiler-explosions, as a member of 
the U. S. Board appointed for that purpose, made nu- 
merous experiments of this nature, but never succeeded 
in producing an explosion. The danger would seem to 
be, fortunately, less than it might be, judging from the 
above. The introduction of feed -water into the steam- 
space of boilers, producing sudden removal of pressure 
from the surface of the water is sometimes supposed to 
have caused explosions. The explosion of a battery of 
several boilers simultaneously — not an infrequent case — 
is supposed to be attributable to the action described 
above, following the rupture of some one of the set. 

Mr. J. G. Heaffman, writing in 1867,* anticipated 
Mr. Lawson's idea, and, after describing an explosion of 

* :> Journal of Assoc, of German Engineers, 1867 ; Iron Age, 1S67. 






CORROBORA TOR Y E VIDENCE. 5 7 

a bleaching boiler, to which the steam was supplied 
from a separate steam-boiler, attributed the catastrophe 
to impact of water against the shell, or the accidental 
production of an opening at the manhole, and asserts 
that explosions thus occur not only from excess of 
pressure, but also from shock. He further states that, 
in accordance with a request made by the Association 
of German Engineers, a commission of the Breslau 
Association experimenting with a small glass boiler, 
found that when the escape-pipes are only gradually 
opened, and the steam allowed gradually to escape, the 
generation of steam quietly continues and the water re- 
mains tranquil. But if the valve is quickly opened, 
steam bubbles suddenly form all through the water, and 
rising to the surface, produce violent commotion. In 
one of these experiments it was his duty to watch the 
manometer, while another person quickly opened the 
valve to allow the steam to escape. As soon as the 
valve was opened the pressure fell 3 lbs., but imme- 
diately again began to rise and the boiler exploded. 
Where it had been in contact with the water it was 
shattered to powder, which lay around like fine sand. 
Of the entire boiler only a few small pieces of the size 
of a dollar were left. Afterward they constructed a 
similar glass boiler w r ith a cylinder 7 inches in diameter, 
and 9 inches in length, and to the ends metal heads 
were fastened ; in the heads were pipes for leading in 
the steam. By means of a force pump the boiler was 
filled with boiling water, the valve being left open 
meanwhile, in order that its sides might become evenly 



5 8 STEAM BOILER EXPLOSIONS. 

heated. Then half the water was drawn off and air let 
in, and afterward more boiling water forced in, so that 
the air was compressed, until the boiler exploded at a 
pressure of 15 atmospheres. 

The report was not nearly as loud as at the former 
explosion, which took place at a pressure of only 3 at- 
mospheres, and the glass was only broken into several 
pieces. This, Mr. Heaffman considers, proves that 
the action of the water on the boiler is such as would 
be produced by exploding nitro-glycerine in the water. 

He goes on to state that, in bleacheries, dye works, 
etc., the habit often prevails of suddenly opening the 
steam-cocks, thus endangering the boiler. He does not 
assert that every time a cock is suddenly opened an 
explosion must follow; but that it may take place 
experience has shown. In the experiments above 
described they had many times opened the glass boiler 
without causing an explosion ; with the second boiler, 
too, they had done so without being able to bring about 
explosion ; both with high and low pressure. In the 
former class of explosions, the steam shatters, twists and 
contorts the parts in an instant. 

" Water-hammer " has, by the bursting of steam- 
pipes, by a process somewhat closely related to that 
described by Clark and Colburn, sometimes caused 
fatal injury to those near at the instant of the accident. 
This is a phenomenon which has long been familiar to 
engineers, and the Author has been cognizant of many 
illustrations, in his own experience, of its remarkable 
effects, and has sometimes known of almost as serious 



CORROBORA TOR Y E VIDENCK. 



59 



losses of life as from boiler-explosions. It is rarely the 
cause of serious loss of property. 

When a pipe contains steam under pressure, and has 
introduced into it a body of cold water, or when a 
cold pipe, containing water, is suddenly filled with 
steam, the contact of the two fluids, even when the 
water is in very small quantities, results in a sudden 
condensation which is accompanied by the impact of 
the liquid upon the pipe with such violence as often to 
cause observable, and very heavy, shocks ; and, often, a 
succession of such blows is heard, the intensity of which 
are the greater as the pipe is heavier and larger, and 
which may be startling and even very dangerous. It is 
not known precisely how this action takes place, but the 
author has suggested the following as a possible outline 
of this succession of phenomena : # 

The steam, at entrance, passes over, or comes in 
contact with, the surface of the cold water standing in 
the pipe. Condensation occurs, at first very slowly, 
but presently more quickly, and then so rapidly that 
the surface is broken, and condensation is completed 
with such suddenness that a vacuum is produced. The 
water adjacent to this vacuum is next projected vio- 
lently into the vacuous space, and, filling it, strikes on 
the metal surfaces, and with a blow like that of a solid 
body, the liquid being as incompressible as a solid. The 
intensity of the resulting pressure is the greater as the 

* Water-hammer in Steam-pipes ; Trans. Am. Soc. Mech. Engrs. ; 
vol. iv. p. 404. 



60 STEAM BOILER EXPLOSIONS. 

distance through which the surface attacked can yield 
is the less, and enormous pressures are thus attained, 
causing the leakage of joints, and even the straining, 
twisting and bursting of pipes. In some cases, the 
whole of an extensive line or system of pipes, has been 
observed to writhe and jump about to such extent as to 
cause well-grounded apprehensions. 

The Author once had occasion to test the strength of 
pipes which had been thus already burst. They were 8 
inches in diameter (20.32 cm.) and ofa thickness of ^ inch 
(0.95 cm.) and had been, when new, subjected to a press- 
ure of about 20 atmospheres (300 lbs. per square inch). 
When tested by the Author in their injured condition, 
they bore from one-third more to nearly four times as 
high pressures, before the cracks which had been pro- 
duced were extended. It is, perhaps, not absolutely 
certain that some of these pieces of pipe may not have 
been cracked at lower pressures than the above ; but it 
is hardly probable. It seems to the Author very certain 
that the pressures attained in his tests were approxi- 
mately those due to the water-hammer, or were lower. 
The steam-pressure had never exceeded about four at- 
mospheres (60 lbs. per sq. in). 

It is evident that it is not safe, in such cases, to cal- 
culate simply on a safe strength based on the proposed 
steam-pressures, but the engineer may find those actually 
met with enormously in excess of boiler-pressure, and a 
" factor- of- safety " of 20 may prove too small, it being 
found as above, that the water-hammer may produce 



ENERGY STORED IN HE A TED METAL. 61 

local pressure approaching, if not exceeding, 70 atmos- 
pheres (1000 lbs. per sq. inch). 

These facts, now well ascertained and admitted, lend 
strong confirmation to the Clark and Colburn theory of 
explosions. 

15. Energy Stored in Heated Metal is vastly less in 
amount, with the same range of temperature, than in 
water. The specific heat of iron is but about one-ninth 
that of water, and the weight of metal liable to become 
overheated in any boiler is very small. If the whole 
crown-sheet of a locomotive boiler were to be heated to 
a full red-heat, it would only store about as much heat, 
per degree, as forty pounds (18 kgs.) of water, or not 
far from 3000 thermal units (756 calories), or 2,316,000 
foot-pounds (33,000 kilog-m., nearly), or about three- 
tenths of the total energy of the fluids concerned in an 
explosion. It would be sufficient, however, to consider- 
ably increase the quantity of steam present in the steam - 
space ; and this increase, if suddenly produced, and too 
quickly for the prompt action of the safety-valve, might 
evidently precipitate an explosion, which would be 
measured in its effects by the total energy present. 

It thus becomes at once obvious that the danger from 
the presence of this stock of excess energy is deter- 
mined not only by the weight of metal heated and its 
temperature, but even more by the rate at which that 
surplus heat is communicated to the water that may be 
brought in contact with it, by pumping in feed-water, 
or by any cause producing violent ebullition. It is 
probable that this cause has sometimes operated to pro- 



_ 



62 STEAM BOILER EXPLOSIONS. 

duce explosions ; but oftener, that the loss of strength 
produced by overheating is the more serious source of 
danger. It is also evident that the first is the more 
dangerous, as the pressures are lower, the second with 
high pressures. 

As illustrating a calculation in detail, assume 

) *4 4 C f crown-sheet, or boiler shell, 

( 25 square feet ) 

overheated \ 1 77 c the metal beincr 

( 1,000 degrees F. ) fa 

) '"•> n > . . > in thickness and its total weight 

X 3/q inch 5 5 

\ ' 1" > Then the product of weight into 

c 375 pounds. ) 

range of temperature, into specific heat (o. in) is the 
measure of the heat-energy stored. 

375X1000X0.111=41,667 B. T. U., nearly; 
170X 556X0.111 = 10,502 calories " 

and in mechanical units, 

41,667X772 =32,167,924 foot-pounds, nearly; 
10,502X423.55=4,448,122 kilog-metres, nearly, 

which is fifteen or twenty times the energy stored in the 
steam in a locomotive boiler in its normal condition, and 
about one-half as much as ordinarily exists in water and 
steam together. It is evident that the limit to the destruc- 
tiveness of explosions so caused is the rate of transfer of 
this energy to the water thrown over the hot plate, 



THE STRENGTH OE HEATED METAL. 6$ 

and the promptness with which the steam made can be 
liberated at the safety-valve. A sudden dash of water 
or spray over the whole of such a surface might be 
expected to even produce a " fulminating explosion." 
Fortunately, as experience has shown, so sudden a 
transfer, or so complete a development of energy, rarely, 
perhaps never, takes place. 

16. The Strength of Heated Metal is known usually 
to decrease gradually with rise in temperature, until, as 
the welding or the melting point, as the case may be, is 
approached, it becomes incapable of sustaining loads. 
Both iron and steel, however, lose much of their tena- 
city at a bright red heat; at which point they have 
less than one-fourth that of ordinary temperature. A 
steam-boiler in which any part of the furnace is left un- 
protected by the falling of the water-level, is very 
likely to yield to the pressure, and an explosion may 
result from simple weakness. At temperatures well be- 
low the red-heat, this will not happen. 

17. Low Water, in consequence of the obvious 
dangers which attend it and the not infrequent 
narrow escapes which have been known, has often 
been, by experienced engineers, considered to be the 
most common, even the almost invariable, cause of ex- 
plosions. This view is now refuted by statistics and a 
more extended observation and experience ; but it re- 
mains one of the undeniable sources of danger and 
causes of accident. 

Its origin is usually in some accidental interruption of 
the supply of feed-water; less often an unobserved leak 



64 STEAM BOILER EXPLOSIONS. 

or accelerated production of steam. Whatever the 
cause, the result is the uncovering of those portions of 
the heating-surface which are highest, and their ex- 
posure, unprotected by any efficient cooling agency, to 
the heat of the gases passing through the flue at that 
point. Should it be the case of a locomotive, or other 
boiler, having the crown-sheet of its fire-box so placed 
as to be first exposed, when the water-level falls, the 
iron may become heated to a full red-heat; if the 
highest surfaces are those of tubes, through which 
gases approximating the chimney in temperature are 
passing, the heat and the danger are less. In either 
case, danger is incurred only when the temperature be- 
comes such as to soften the iron, or when the return of 
the water with considerable rapidity gives rise to the 
production of steam too rapidly to be relieved by the 
safety-valve or other outlet. Such explosions probably 
very seldom actually occur, even when all conditions 
seem favorable. Every boiler-making establishment is 
continually collecting illustrations of the fact that a 
sheet may be overheated, and may even alter its form 
seriously, when overheated, without completely yielding 
to pressure, and the Author has taken part in many at- 
tempts to experimentally produce explosions by pump- 
ing feed-water into red-hot boilers, and has but once 
seen a successful experiment. The same operation in 
the regular working of boilers has been often performed 
by ignorant or reckless attendants without other dis- 
aster than injury to the boiler; but it has unquestion- 
ably, on other occasions, caused terrible loss of life and 






LOW WATER. 65 

property. The raising of a safety-valve on a boiler in 
which the water is low, by producing a greater violence 
of ebullition in the water on all sides the overheated 
part, may throw a flood of solid water or of spray over 
it ; and it is possible that this has been a cause of many 
explosions. The Author has seen but a single explosion 
produced in this way, although he has often attempted 
to produce such a result. In three experiments on a 
certain cylindrical boiler, empty, and heated to the red- 
heat, the result of rapidly pumping in a large quantity 
of water was, in the first, the production of a vacuum, 
in the second an excess of pressure safely and easily 
relieved by the safety-valve ; and in the third case a 
violent explosion of the boiler and the complete de- 
struction of the brick setting.* The boiler experi- 
mented upon was set in brickwork in the usual man- 
ner. In each experiment, the boiler was filled with 
water, a fire started, and, when the fire was in good 
order and the steam at the right point, all water was 
blown out ; the boiler was allowed to become heated to 
the desired temperature, as indicated by a pyrometer 
inserted within it, and, at the proper moment, the feed- 
water was introduced by a force-pump. At each occa- 
sion, on the introduction of the water, the steam-press- 
ure rose suddenly, the safety-valve opened, and, the 
water still continuing to enter, the boiler-pressure 
dropped almost as rapidly as it had risen, and the boiler 
cooled down on each occasion (except the last) without 

*Sci. Am., Sept. 1875. 



66 STEAM BOILER EXPLOSIONS. 






apparent injury, and without having even started a 
seam, although the metal had been red hot. 

The last experiment resulted in the explosion of the 
boiler and the destruction of its setting, and interrupted 
the work. The succession of phenomena was in this 
case precisely as already described ; but the tempera- 
ture of the boiler was on this occasion higher, probably 
a bright red on the bottom, and the pressure of steam 
was about 60 lbs. before the explosion occurred. It had 
fallen somewhat from the maximum, attained the mo- 
ment before. A committee of the Franklin Institute, 
conducting similar experiments, t had the same exper- 
ience, the pressure " rising from one to twelve atmos- 
pheres within ten minutes," after starting the pump. 
The most rapid vaporization occurs, as is well known, at 
a comparatively low temperature of metal ; at high 
temperature the spheroidal condition is produced, and 
no contact exists between metal and liquid. 

Mr. C. A. Davis, President of the New York and Bos- 
ton Steamboat Co., in a letter addressed, Dec. 7, 183 1, 
to the Collector of the Port of New York, and con- 
cerning inquiries of the U. S. Treasury Department, 
wrote : # 

" I have noted that by far the greater number of ac- 
cidents by explosion and collapsing of boilers and flues, 
I might say seven-tenths, have occurred either while the 
boat was at rest, or immediately on starting, particu- 

f Journal Franklin Inst., 1837, vol. 17. 
* Report of Steam Boilers, H. R., 1832. 



LOW WATER. 67 

larly after temporary stoppages to take in or land pas- 
sengers. These accidents may occur from directly 
opposite causes, either by not letting off enough steam, or 
by letting off too much; the latter is by far the most de- 
structive." 

The idea of this writer was that the " letting off of 
too much " steam, by producing low water, was the most 
frequent cause of explosions, an idea which has never 
since been lost sight of. 

The chief engineer of the Manchester (G. B.) Steam 
Boiler Association, in 1866-7 repeatedly injected water 
into overheated steam-boilers, but never succeeded in 
producing an explosion. # Yet, as has been seen, such 
explosions may occur. 

A writer in the Journal of the Franklin Institute^ a 
half century or more ago, asserted that " the most 
dreadful accidents from explosions which have taken 
place, have occurred from low-pressure boilers/' It 
was, as he states, " a fact that more persons had been 
killed by low than by high-pressure boilers." Nearly all 
writers of that time attributed violent explosions to low 
water, and some likened the phenomenon to that ob- 
served when the blacksmith strikes with a moist ham- 
mer on hot iron. 

Thus, if the boiler is strong, and built of good iron, 
and not too much overheated, or if the feed-water is in- 
troduced slowly enough, it is possible that it may not 



* Mechanics' Magazine, May, 1867. 
fVol. 3; pp. 335, 418, 420. 



68 STEAM BOILER EXPLOSIONS. 

be exploded ; but with weaker iron, a higher tempera- 
ture, or a more rapid development of steam, explosion 
may occur. Or, if the metal be seriously weakened by 
the heat, the boiler may give way at the ordinary or a 
lower pressure, which result may also be precipitated by 
the strains due to irregular changes of dimension ac- 
companying rapid and great changes of temperature. 
Explosions due to low water, when there is a consid- 
erable mass of water below the level of the overheated 
metal, are sometimes fearfully violent, a boiler com- 
pletely emptied of water, and only exploded by the 
volume of steam contained within it, is far less danger- 
ous. Low water and red-hot metal in a locomotive or 
other fire-box boiler, are, for this reason, far more dan- 
gerous than in a plain cylindrical boiler; as was indica- 
ted by the experiments conducted by the Author, the 
latter must be entirely deprived of water before this 
dangerous condition can arise. In the course of the nu- 
merous experiments already alluded to, many attempts 
were made to overheat the latter class of boiler, but none 
were successful until the water was entirely expelled. 
Experiments, with apparatus devised for the purpose of 
keeping the steam moist under all circumstances, indi- 
cate that it is difficult, if not impossible, to overheat 
even an uncovered fire-box crown -sheet, if the steam 
be kept moist, and that such steam is very nearly as 
good a cooling medium, in such cases, as the water 
itself. 



LOW WATER. 



69 



Figure 5 # represents a boiler exploded by the intro- 
duction of water, after it had been emptied by care- 
lessly leaving open the blow-cock. This boiler was 




Fig. 5.— Boiler Exploded ; Cause, Low Water. 

about five years old, and the explosion, as is usual in 
such cases, was not violent, the small amount of water 
entering and the weakness of the sheet conspiring to 
prevent the production of very high pressure, or the 
storage of much energy. The whole of the lower part 
of the shell of the boiler was found, on subsequent ex- 
amination, to have been greatly overheated. One man 
was killed by the falling of the setting upon him ; no 
other damage was done. 

Figure 6 shows the effect of a similar operation on a 
water-tube boiler. The feed-water was cut off, and not 



' The Locomotive ; Sept. 1886 ; p. 129. 



7 o STEAM BOILER EXPLOSIONS. 

noticed until the water-level became so low that the 
boiler was nearly empty and the tubes were overheated. 
One of the tubes burst, and the damage was speedily 



Fig. 6. — Tube Burst ; Low Water. 

repaired at a cost of $15, and the works were running 
the next day.* 

That low water and the consequent overheating of 
the boiler does not necessarily produce disaster, even 
when the water is again supplied before cooling off, 
was shown as early as 181 1, by the experience of Cap- 
tain E. S. Bunker of the Messrs. Stevens's steamboat 
" Hope," then plying between New York and Albany. 
During one of the regular passages, he discovered that 
the water had been allowed, by an intoxicated fireman, 
to completely leave both the boilers. He at once 
started the pump and, filling up the boilers, proceeded 
on his way, no other sign of danger presenting itself 
than " a crackling in the boiler as the water met the 
hot iron, the sound of which was like that often heard 
in a blacksmith's shop when water is thrown on a piece 
of hot iron." t A year later, Captain Bunker repeated 
this experience, at Philadelphia, on the " Phoenix," 

*G. H. Babcock. 

f Doc. No. 21, H. R., 25th Congress, 3rd Session, 1838, p. 103. 



LOW WATER. 



71 



where the boilers where of the same number and size 
as those of the " Hope." * 

Defective circulation may cause the formation of a 
volume of steam in contact with a submerged portion 
of the heating surface. The Author, when in charge of 
naval engines during the civil war, 1 861-5, found it pos- 
sible, on frequent occasions to draw a considerable 
volume of practically dry steam from the water-space 
between the upper parts of two adjacent furnaces at a 
point two or three feet below the surface-water level. 
After drawing off steam for a few seconds, through a 
cock provided to supply hot water for the engine and 
fire-rooms, water would follow as in the normal condi- 
tion of the boiler. This condition often occurs in some 
forms of boiler and has been occasionally observed by 
every experienced engineer. It would not seem im- 
possible, therefore, that steam might be sometimes thus 
encaged in contact with the furnace, and thus cause 
overheating of the adjacent metal. Many such in- 
stances have been related, but they have been com- 
monly regarded by the inexperienced as somewhat 
apochryphal.t 

In order that the danger of overheating the crown- 
sheet of the locomotive type of boiler may be lessened, 
it is very usual to set it lower at the fire-box end, when 
employed as a stationary boiler, so as to give a greater 
depth of water over the crown-sheet than over the 

♦Ibid. 

f See London Engineer, Dec. 7, i860, pp. 371, 403. 



7 2 STEAM BOILER EXPLOSIONS. 

tubes at the rear. The plan of giving greatest depth of 
water, when possible, at that end of the boiler at which 
the heating-surfaces near the water-surface are hottest, is 
always a good one. 

Mr. Fletcher concluded from his experiments that 
low water is only a cause of danger by weakening the 
overheated plates. He says : # 

"These experiments, it is thought, may be accepted 
as conclusive that the idea of an explosion arising from 
the instantaneous generation of a large amount of steam 
through the injection of water on hot plates is a fallacy." 

The conclusion of the Author, in view of the experi- 
ments of the committee of the Franklin Institute and of 
his own personal experience in the actual production of 
explosions by this very process, as elsewhere described, 
does not accord with the above ; but it is sufficiently 
well established that low water may frequently occur 
and feed-water may be thrown upon the overheated 
plate without necessarily causing explosion. Danger 
does, however, certainly always arise, and such explo- 
sions have most certainly occurred — possibly many in 
the aggregate. 

Low-water is certainly very rarely, perhaps almost 
never, the cause of explosion of other than fire-box 
boilers ; in these, however, the danger of overheating 
the crown-sheet of the furnace, if the supply of water 
fails, is very great, and, in such cases, explosion is always 
to be feared. The most disastrous explosions are usually 

* London Engineer, March 15, 1867, p. 228. 






SEDIMEN T A ND I NCR US TA TION. 7 3 

those, however, in which the supply of water is most 
ample. 

18. Sediment and Incrustation sometimes produce 
the effect of low- water in boilers, even where the surfaces 
affected are far below the surface of the water. Every 
increase of resistance to the passage of heat through the 
metal and the encrusting layer of sediment or scale 
causes an increase of temperature in the metal adjacent 
to the flame or hot gases, until, finally, the incrustation 
attaining a certain thickness, the iron or steel of the 
boiler becomes very nearly as hot as the gases heating 
it. Should this action continue until a red-heat, or a 
white-heat, even, as sometimes actually occurs, is 
reached, the resistance becomes so greatly reduced that 
the sheet yields, and either assumes the form of a 
" pocket," or depression, as often happens with good 
iron and with steel; or it cracks, or it even opens suffi- 
ciently to cause an explosion. " Pockets" often form 
gradually, increasing in depth day by day, until they 
are discorered, cut out, and a patch or a new sheet put 
in, or until rupture takes place. In such cases, the 
incrustation keeps the place covered while permitting 
just water enough to pass in to cause the extension of 
the defect. 

In some cases, the process is a different and a more 
disastrous one. The scale covers an extended area, 
permitting it to attain a high temperature. After a time 
a crack is formed in the scale by the unequal expansion 
of the two substances and the inextensibility of the 
incrustation ; and water entering through this crack is 



74 STEAM BOILER EXPLOSIONS. 

exploded into steam, ripping off a wide area of incrusta- 
tion previously covering the overheated sheet, and giv- 
ing rise instantly, probably, to an explosion which 
drives the sheet down into the fire, and may also rend 
the boiler into pieces, destroying life and property, on 
every side. Such an explosion usually takes place with 
the boiler full of water and its stored energy a maximum, 
and the result is correspondingly disastrous. 

Certain greasy incrustations, and some flowery forms 
of mineral or vegetable deposits, have been found 
peculiarly dangerous, as, in even exceedingly thin 
layers, they are such perfect non-conductors as to 
speedily cause overheating, strains, cracks, leakage, and, 
often, explosion. M. Arago mentions a case in which 
rupture occurred in consequence of the presence of a rag 
lying on the bottom of a boiler. # 

The effect of incrustation in causing the overheating 
of the fire-surfaces, the formation of a " pocket," and 
final rupture, is well shown in the three illustrations 
which follow. 

When the water is fully up to the safe level, as at the 
right in the first of the three figures, the heat received 
from the furnace gases is promptly carried away by the 
water and the sheet is kept cool. When the water falls 
below that level, or is prevented, by incrustation, from 
touching the metal, as in the left-hand illustration, the 
sheet becomes red-hot, soft, and weak, and yields as 
shown. When this goes on to a sufficient extent, as on 

* Report of the Committee of the Franklin Institute. 



SEDIMENT AND INCRUSTATION. 



7S 





Fig. 7. — Overheating the Sheet. 

a horizontal surface, figure 8, a pocket is produced. The 
illustration represents a sheet removed from the shell 




Fig. 8.— A u Pocket." 

of an externally fired boiler, thus injured. 

Finally, when the defect is not observed and the 
injured sheet removed, the metal may finally give way 
entirely, permitting the steam and water to issue, as in 
the last illustration of this series, in which the last step 




Fig. 9. — Ruptured Pocket. 



7 6 



STEAM BOILER EXPLOSIONS. 



in the process is well represented. Where the area thus 
affected is considerable, the result may be a general 
breaking up of that portion of the shell, as in the next 
figure, and an explosion may prove to be the final step 




;_FiG^io.— Shell lRupxures^.,^^. 

in the chain of phenomena described. In other cases 
where, as in the next sketch, a line of weakness may be 



...A.. 




Fig. ii. — Extended Rupture. 



the result of other causes; a large section of the boiler 
may be broken out, as at A D, Figure 1 1. 

The deposition of sediment and of scale takes place 
in the boiler. Not only in the boiler, but also with 
some kinds of water in the feed-pipe, as is illustrated in 



SEDIMENT AND INCRUSTATION. 77 



Fjg. 12. — Incrustation in Feed-pipe. 

the accompanying engraving, which is made from an 
actual case in which the pipe was so nearly filled as to 
become quite incapable of performing its office. A cur- 
rent has apparently no effect, in many such cases, in 
preventing the deposition of scale. The Author has 
known hard scale to form in the cones of a Giffard in- 
jecter under his charge, where the steam was moving 
with enormous velocity, and loudly whistling as it 
passed. 

Instances are well known of the explosion, with fatal 
effect of open vessels, in consequence of the action above 
described. Mr. G. Gurney, in 1 831, gave an account of 
such an explosion of the water in an open cauldron at 
Meux's brewery, by which one person was killed and 
several others injured. # It was found that the bottom 
had become encrusted with sediment, and the sudden 
rupture of the film, permitting contact of the water 
above with the overheated metal below, caused such a 
sudden and violent production of steam that it actually 

* Report on Steam Carriages ; Doc. 101, 22nd Congress, 1st Session, 
P- 31. 



7 8 STEAM BOILER EXPLOSIONS. 

ruptured the vessel. The process of which this is an 
illustration is precisely analogous to suddenly throwing 
feed-water into an overheated boiler. 

19. Energy Stored in Superheated Water has been 
sometimes considered a source of danger to steam boil- 
ers and a probable cause of explosions. The magni- 
tude of this stock of energy is not likely to differ 
greatly from that of water at the same temperature un- 
der the pressure due that temperature, and, for present 
purposes, it may be taken as approximately unity. The 
quantity of heat so stored is, therefore, measured very 
nearly by the product of the weight of water so over- 
heated, the mean range of superheating, and the specific 
heat here taken as unity. It is not known how large a 
part of the water in any boiler can be superheated, or 
the extent to which this action can occur. It is to be 
doubted, however, whether it can take place at all in 
steam-boilers. 

To secure this condition the experiment of M.M. 
Donny, Dufour, and others show that the larger the 
mass of water, the less the degree of superheating attain- 
able; the more impure the water, or the greater the 
departure from the condition of distilled water, and the 
larger the proportion of air or sediment mechanically 
suspended, the more difficult is it to attain any consid- 
erable superheating. 

As early as 18 12 * Gay-Lussac observed a retarda- 

* Ann. de Chemie et de Physique, lxxxii. 



ENERGY STORED IN SUPERHEATED WATER. 79 

tion of ebullition in glass vessels ; thirty years later,* 
M. Marcet found that water, deprived of air, can be raised 
several degrees above its normal boiling point, while 
Donny,t Dufour,{ Magnus,^ and Grove tt all succeeded 
in developing this phenomenon more or less remark- 
ably. Donny, sealing up water, deprived of air, in 
glass tubes, succeeded in raising the boiling point to 
138° C. (280 F.), at which temperature vaporization 
finally occurred explosively. Dufour, by floating glo- 
bules of pure water in a mixture of oils of density 
equal to that of the water, succeeded with very minute 
globules, in raising the boiling point to 173 C. 
(347 F.) at which temperature the normal tension of 
its steam is 1 1 5 pounds per square inch (nearly 8 at- 
mospheres) by gauge. In such cases, the touch of any 
solid, or of bubbles of gas, would produce explosive 
evaporation. Solutions always boil at temperatures 
somewhat exceeding the boiling point of water, but 
usually quietly and steadily. In all these cases, the 
rise in temperature seems to have been greater the 
smaller the mass of water experimented with. 

In all ordinary cases of steam-boiler operation, the 
mass of water is simply enormous as compared with the 
quantities employed in the above-described laboratory 
experiments; the water is almost never pure, and 
probably as invariably contains more or less air. It 

*Bibl. Univ., xxxviii. 

\ Ann. de Chemie et de Physique, 3ve, Seriet. xvi. 

{Bibl. Univ. Nov. 1861, t. xii. 

§ Poggendorffs Ann., t. cxiv. ffCosmos, 1863. 



80 STEAM BOILER EXPLOSIONS. 

would seem very unlikely that such superheating could 
ever occur in practice. There is, however, some evi- 
dence indicating that it may. 

Mr. Wm. Radley # reports experimenting with small 
laboratory boilers of the plain cylindrical form, and 
continuing slowly heating them many hours, finally at- 
taining temperatures exceeding the normal by 15 F. 
(8. 3 C.) The investigator concludes : 

" Here we have conclusive data suggesting certain 
rules to be vigorously adopted by all connected with 
steam-boilers who would avoid mysterious explosions: 
First, never feed one or more boilers with surplus water 
that has been boiled a long time in another boiler, but 
feed each separately. Second, when boilers working 
singly or fed singly are accustomed, under high pressure, 
to be worked for a number of hours consecutively, day 
and night, they should be completely emptied of water 
at least once every week, and filled with fresh water. 
Third, in the winter season the feed-water of the boiler 
should be supplied from a running stream or well ; thaw 
water should never be used as feed for a boiler." 

" Locomotive, steamboat, and stationary engine boil- 
ers have their fires frequently banked up for hours, 
without feeding-water, and the steam fluttering at the 
safety-valve, so as to have them all ready for starting at 
at a moment. This is a dangerous practice, as the fore- 
going experiments demonstrate. While so standing, 
all the atmospheric air may be expelled from the water, 

:: " London Mining Journal, June 28, 1856. 









ENERGY STORED IN SUPERHEATED WATER, 81 

and it may thereby attain to a high heat, ready to gen- 
erate suddenly a great steam- pressure when the feed- 
pump is set in motion. This is, no doubt, the cause of 
the explosion of many steam-boilers immediately upon 
starting the engine, even when the gauge indicates 
plenty of water. The remedy for such explosions must 
be evident to e>very engineer — keep the feed-pump 
going, however small may be the feed required." 

On the other hand, the report of a committee 
appointed by the French Academy to inquire into the 
superheated water theory of steam-boiler explosions, 
indicates at least the difficulty of securing such condi- 
tions.* The committee constructed suitable apparatus, 
experimented in the most exhaustive manner, and 
investigated several explosions claimed by the advocates 
of the theory to have been due to this cause. They 
failed to superheat water under any conditions which 
could probably occur in practice, and the explosions 
investigated were shown conclusively to have resulted 
from simple deterioration of the boilers, or from care- 
lessness. 

It is unquestionably the fact that explosions due to 
this cause are at least exceedingly rare, although it is 
not at all certain that they may not now and then take 
place. The ocean is constantly being traversed by 
thousands of steamers having surface condensers and 
boilers in which the water is used over and over again, 
and in which is every condition seemingly favorable to 

*Annales de Mines, 1886. 



82 STEAM BOILER EXPLOSIONS, 

such superheating of the water ; but no one known 
instance has yet occurred of the production of this phe- 
nomenon, there or elsewhere, on a large scale, where 
boilers are in regular operation. 

M. Donny, who first suggested the possibility of 
this action as a cause of boiler-explosions, has had 
many followers. M. Dufour,* who doubts if such ex- 
plosions are possible in the ordinary working of the 
boiler, points out the fact, however, that boilers which 
are quietly cooling down, after the working hours are 
over, are peculiarly well situated for the development of 
this form of stored energy. He points out the known 
fact that many explosions have taken place under such 
conditions, the pressure having fallen below the work- 
ing-pressure. M. Gaudryt makes the same observation. 
Such cases are supposed to be instances of " retarded 
ebullition," with decrease of pressure and superheating 
of the water. Many circumstances unquestionably tend 
to strengthen this view. 

So tremendous are the effects of many explosions 
that M. Andrand has expressed the belief that a true 
explosion must be preceded by pressure approaching or 
exceeding 200 atmospheres,:): an intensity of pressure, 
however, which no boiler could approximate. Mr. Hall, 
also, thinks that the shattering effect sometimes wit- 
nessed, resulting in the shattering of a boiler into small 

*Sur l'Ebullition de l'Eau, et sur une cause probable d'Explosion des 
Chandiers a vapeur, p. 29. 

f Traite des Machines a Vapeur. 
jComptes Rendes, May 1855, p. 1062. 



ENERGY STORED IN SUPERHEATED WATER. 83 

pieces, must be the effect of a sudden and enormous 
force partaking of the nature of a blow,* and cites cases, 
such as are now known to be common, of an explosion 
taking place on starting an engine after the boiler has 
been at rest and making no steam for a considerable 
time. M. Arago cites a number of similar instances,t 
and Robinson a number in still greater detail.J Boilers, 
after quietly " simmering " all night, exploded at the 
opening of the throttle- valve or the safety-valve in the 
morning. The locomotive "Wauregan," which exploded 
within sight and hearing of the Author, at Providence, 
R. I.,in February, 1856, is mentioned by Colburn as such 
a case. The engine had been quietly standing in the en- 
gine house two hours, the engineer and fireman engaged 
cleaning and packing, preparatory to starting out. The 
explosion was without warning and very violent, strip- 
ping off the shell and throwing it up through the roof, 
and killing the engineer, who was standing beside his 
engine. 

Mr. Robinson^ thinks the usual cause of such explo- 
sions is the overheating of the water, the phenomenon 
being in its effects very like the " water-hammer " in 
steam-pipes, producing shocks which the Author has 
shown to give rise to instantaneous pressures exceeding 
the working-pressures ten or twenty times ; the action, 

* Civil Engineers' Journal, 1856, p. 133 ; Dingler's Journal, 1856, 
p. 12. 

fAnnuaire, 1830. 

J St. Boiler Explos., p. 62. 

§ Ibid, p. 66, 



84 STEAM BOILER EXPLOSIONS. 

however, seems rather to be that " boiling with bumping " 
familiar to chemists handling sulphuric acid in consider- 
able quantities. Instances have been known in which 
this bumping has burst pipes or severely shaken boilers 
and setting without producing explosion. 

The de-aeration of water, and the subsequent super- 
heating of the liquid, to which some explosions have 
been attributed, are phenomena which have been often 
investigated. Mr. A. Guthrie, formerly U. S. Super- 
vising Inspector General of Steam-vessels, states that he 
made many such experiments, as follows: * 

" (i.) In my experiments, I first procured a sample 
of water from the boiler of an ordinary condensing en- 
gine; here, of course, in addition to being subjected to 
long-continued boiling, it had passed through the va- 
cuum. 

(2.) I procured a sample from the ordinary high 
pressure non-condensing engine boiler, which before 
entering the boiler had passed the heater at 210 . 

(3.) I procured some clean snow and dissolved it 
under oil, so that there was no contact with the air. 

(4.) I froze some water in a long, upright tube, using 
only the lower end of the ice when removed from the 
tube, and dissolved under oil. 

(5.) I placed a bottle of water under a powerful va- 
cuum pump worked by steam, for two hours; agitating 
the water from time to time to displace any air that 
might possibly be confined in it, then closed it by a 
stop-cock, so that no air could possibly return. 

* American Artisan ; Locomotive, 1880. 



ENERGY STOKED IN SUPERHEATED WATER. 8j 

(6.) I boiled water in an open boiler for several 
hours, and filled a bottle half full, closed and sealed it 
up, so that when it became cool it would in effect be un- 
der a vacuum, agitating it as often as seemed necessary. 

(7.) Another bottle was filled with the same, and 
sealed. 

(8.) I next took some clean, solid ice, dissolved it 
under oil, and brought it to a boil, which was continued 
for an hour or more, after which it was tightly corked. 

(9.) I procured a bottle of carefully distilled water, 
after long boiling and having been perfectly excluded 
from air during the distillation. 

(10.) I obtained a large number of small fish, placed 
them in pure, clean water in an open-headed cask on a 
moderately cold night, so that very soon it became 
frozen over, consequently excluding the air, the fish 
breathing up the air" in the water, so that (if I am cor- 
rect in this- theory) a water freed from air would be the 
result ; but in some of these different processes, if not 
in all, I was likely to free the water from air, if it could 
ever possibly occur in the ordinary course of operating 
a steam boiler. 

Having procured a good supply of glass boilers 
adapted to my purpose, and so made that the slightest 
changes could be noted, and using as delicate thermome- 
ters as I could obtain, I took these samples one after 
another, and brought them to the boiling point; and 
every one, with no variation whatever, boiled effectually 
and positively at 2 1 2° Fahrenheit or under ; nor was 



86 STEAM BOILER EXPLOSIONS. 

there the slightest appearance of explosion to be ob- 
served." 

This evidence is, of course, purely negative. 

The superheating of water, on even the small scale of 
the laboratory experiments of Donny, Dufour and others, 
has never been successfully performed except with the 
most elaborate precautions. The vessel containing the 
liquid must be absolutely clean ; the washing of all sur- 
faces with an alkaline solution seems to be one of the 
customary preliminary operations. The vessel must 
usually be heated in a bath of absolutely uniform tem- 
perature in order that currents may not be set up within 
the body of the liquid to be heated ; no solid can be 
permitted to enter or come in contact with it; no shock 
can be allowed to affect it ; even contact with a bubble 
of gas may stop the process of superheating. All these 
conditions are as far removed as possible from those 
existing in steam-boilers. 

20. The Spheroidal State, or Leidenfrost's phe- 
nomenon, as it is often called, is a condition of the 
water, as to temperature, precisely the opposite of that 
last described, its temperature being less, rather than 
greater, than that due the pressure ; while the adjacent 
metal is always greatly overheated, and thus becomes a 
reservoir of surplus heat-energy which can be trans- 
ferred, at any instant, to the water. This peculiar phe- 
nomenon was first noted by M. Leidenfrost about 1746. 



THE SPHEROIDAL STATE. 87 

It was studied by Klaproth, Rumford, and Baudrimont, # 
and more thoroughly by Boutigny. 

When a small mass of liquid rests upon a surface of 
metal kept at a temperature greatly exceeding the boil- 
ing point of the liquid under the existing pressure, the 
fluid takes the form of a globule if a very small mass, 
or of a flattened spheroid or round-edged disk if of 
considerable volume, and floats around above the metal, 
quite out of contact with the latter, and gradually, very 
slowly, evaporates. The higher the temperature of the 
plate, the more perfect this repulsion of the liquid. 
Should the temperature of the metal fall, on the other 
hand, the globule gradually sinks into contact with it, 
and, at a temperature which is definite for every liquid, 
and is the lower as it is the more volatile, finally sud- 
denly absorbs heat with great rapidity and evaporates 
often almost explosively. If contact is forcibly produced 
at the higher temperature of the supporting plate of 
metal, as under a blacksmith's hammer, a real explosion 
takes place, throwing drops of the liquid in every direc- 
tion. 

M. Boutigny found the temperature of contact to be, 
for water, alcohol, and ether, respectively, 142 C, 134 
and 6i° (287 F., 273, and 142 ). In all cases, the 
temperature of the liquid was independent of that of 
the metal and somewhat below the boiling point. It is 
found, also, that a real and powerful repulsion is pro- 
duced between metal and liquid ; this is supposed to be 

* Ann, de Chemie et de Physique, 2d Series, t. Ixi, 



88 STEAM BOILER EXPLOSIONS, 

due, in part at least, to the cushion of vapor there 
interposing itself. Contact is accelerated by the intro- 
duction of soluble salts into the liquid. 

It is supposed by many writers that this phenomenon 
may play its part in the production of explosions of 
steam-boilers, and especially in cases in which there 
seems some evidence that, immediately before the explo- 
sion, there was no apparent overheating of the parts 
exposed to the action of the fire, and in those still more 
remarkable instances in which the shattered parts had 
been, to all appearance, much stronger than other por- 
tions which had not been ruptured, no evidence existing 
of low-water or overheating at the furnace, and the 
pressure being, the instant before the accident, at or 
below its usual working-figure. Bourne # has no doubt 
that this does sometimes take place. Colburn gives a 
number of instances of explosions taking place under, 
apparently, precisely similar conditions, and Robinson f 
also cites several, in some of which the plates of the shell 
were badly shattered, as by a concussive force. In some 
such instances, evidence of overheating, but only far 
below the water-level known to have existed immedi- 
ately before the explosion, have been observed, indicat- 
ing repulsion to have there occurred. This latter is 
simply still another instance of bringing about the same 
results as when pumping water into an overheated 
boiler in which the water is low. 

* Treatise on the Steam Engine, 1868. 
f Steam Boiler Explosions, p. 33. 



THE SPHEROIDAL STATE. 89 

Mr. Robinson # tells of a case in which a nearly new 
locomotive, standing in the house, with a pressure, as 
shown but a moment before by the steam-guage, of but 
40 pounds — one-third its presumed safe working-press- 
ure — the fire low and everything perfectly quiet — 
exploded with terrible violence, shattering the top of 
the boiler, directly over the fire-box, into many parts. 
That such explosions might occur, were the metal actu- 
ally overheated under water, is shown by experiences 
not at all uncommon. 

In the work of determining the temperatures of cast- 
ing alloys tested by the Author f for the U. S. Board 
appointed in 1875 to test iron, steel, and other metals, 
at the first casting, composed of 94.10 copper, 5.43 tin, 
while pouring of the metal into the water for the test, 
an explosion took place which broke the wooden vessel 
which held the water, and threw water and metal 
about with great violence. It appears probable that 
the metal was heated to an unusually high temperature, 
as in pouring other metals when at a dazzling white 
heat explosions sometimes took place, but they were 
usually not violent enough to do more than make a 
slight report as the hot metal touched the water. 
Another bar was cast at an extremely high temperature, 
being at a dazzling white heat. On pouring a small 
portion in water in attempting to obtain the tempera- 
ture, a severe explosion took place, and this was repeated 



* Steam Boiler Explosions, p. 62. 

\ Report on Copper-Tin Alloys, Washington, 1879. 



9 o STEAM BOILER EXPLOSIONS. 

every time that even a small drop of the molten metal 
touched the water. The cold ingot mould was then 
filled with this very hot metal. After the metal remain- 
ing in the crucible had stood for several minutes and 
had cooled considerably, it could be poured into water 
without causing the slightest explosion. Thus it would 
seem that the temperature at which contact with the 
water is produced may have an important effect upon 
the violence with which the steam is generated, and also 
that of the explosion so produced. The explosions some- 
times taking place with fatal effect in foundries when 
molten metal is poured into damp or wet moulds are 
produced in the manner above illustrated. They are 
usually apparently of the "fulminating class." Another 
instance occurred within the cognizance of the Author, 
even more striking than either of the above. * 

Feb. 2, 1 88 1, two workmen in a gold and silver 
refinery were engaged in "graining" metal, which pro- 
cess consists in pouring a small stream of melted metal 
into a barrel of water, while a stream of water is also 
run into the barrel to agitate the water already there. 
Suddenly an explosion occurred which literally shivered 
the barrel and threw the workmen across the room. 
Every hoop of the barrel, stout hickory hoops, was 
broken. The staves, seven-eighths of an inch thick, 
and of oak, were not only splintered but broken across, 
and the bottom, which was resting on a flat surface, and 
which was of solid oak, an inch in thickness, was split 

* Reported in the Providence (R. I.) Journal, Feb. 2, 1881. 



THE SPHEROIDAL STATE. 



9« 



and broken across the grain. A box, on which stood 
the man who was pouring the metal, was converted into 
kindling-wood. The metal, though scattered some- 
what, for the most part remained in place, but the water 
was thrown in all directions. 

This explosion of an open barrel, like the preceding 
cases, was evidently due to the deferred thermal reaction 
of the water with a mass of very highly heated metal, 
with which it was finally permitted to come in contact 
at a temperature which allowed an explosive formation 
of steam. This class of explosions, by which open 
vessels are shattered and the water contained in them 
"atomized" are by many engineers believed to exem- 
plify the terrific " explosions fulminantes " of French 
writers on this subject. The temperature of maximum 
vaporization, with iron plates, was reported by the 
committee of the French Institute to be 346^° F. 
(175 C), and that of repulsion 385 F. (196 C), and 
to be the same under all pressures. Any cause which 
may retard the passage of heat from the iron to the 
water, though but the thinnest film of sediment, grease, 
or scale, may permit such increase of temperature as 
may lead to repulsion of the water, the overheating of 
the metal, the production of the spheroidal condition, 
and the accidents due to that phenomenon, provided 
that the fire be so driven as to supply more heat than 
can be disposed of in ordinary working by the circula- 
tion and vaporization then going on. Robinson's 
experiments with safety-plugs indicate that a good irra- 
diation is usually a sufficient insurance against this 



92 STEAM BOILER EXPLOSIONS. 

action ; and experience with the boilers of locomotives 
and of torpedo-boats, in which from 50 to 100 pounds 
of coal per square foot (244 to 488 kilogs. on the square 
metre) of grate are burned every hour, shows that the 
risk, with clean boilers of good design, is not great. 
With impure water and defective circulation, Robinson 
observed many instances of singular and dangerous 
phases of this action. * It is suggested that many 
explosions of locomotives on the road, or at stations, 
may be due to the impact, on the shells of their boilers, 
of water thus projected from overheated iron below the 
water-line. In many such cases, the engines have not 
left the rails, the break taking place just back of the 
smoke-box, or near the fire-box, and from the impact 
of water thus thrown from the tube-sheets. 

M. Melsen t experimentally proved it possible to pre- 
vent the occurrence of the spheroidal condition by the 
distribution of spurs, or points of iron over the endan- 
gered sheets. 

The conductivity of the metal has been an important 
influence on the effect of contact, suddenly produced, 
between the red-hot solid and the liquid. Professor 
Walter R. Johnson observed, in his elaborate experi- 
ments, $ that brass produced much greater agitation 
of the water when submerged at the red-heat than did 
iron. He also noted the singular fact that water at the 

* See his Steam Boiler Explosions, pp. 40-46. 

■(• Bull, de l'Academie Royale de Belgique, April, 1871. 

\ Reports on Steam Boilers, II . R., 1832, p. in. 



THE SPHEROIDAL STATE. 



93 



boiling point, thrown upon red-hot iron, requires more 
time for evaporation than cold water, probably in con- 
sequence of the greater efficacy of the latter in bringing 
down the temperature of the metal to that of maximum 
rapidity of action. The contact with the iron of 
incrustation, oxide, or other foreign matter, accelerated 
this process, also. Johnson found that, beyond the 
temperature of maximum repulsion, vaporization was 
accelerated by further elevation of temperature. 

At the meeting of the British Association in 1872, 
Mr. Barrett read a paper upon the conditions affecting 
the spheroidal state of liquids and their possible rela- 
tionship to steam-boiler explosions. The presence of 
alkalies or soaps in water perceptibly aids in the production 
of the spheroidal state. A copper ball immersed in 
pure water produced a loud hissing sound and gave off 
a copious discharge of steam. On adding a little soap 
to the water, the ball entered the liquid quietly. Albu- 
men, glycerine, and organic substances generally pro- 
duced the same result. The best method is to use a 
soap solution, and to plunge into this a white-hot cop- 
per ball of about two pounds of weight. The ball 
enters the liquid quietly, and glow white hot at a depth 
of a foot or more beneath the surface. Even against 
such pressure, the ball will be surrounded with a shell 
of vapor an inch in thickness. The reflection of the 
light from the bounding surfaces of the vapor bubble 
surrounding the glowing ball, gives to the envelope the 
appearance of burnished silver. As the ball gradually 
cools, the bounding envelope become thinner, and finally 



94 



STEAM BOILER EXPLOSIONS; 



collapses with a loud report and the evolution of large 
volumes of steam. Mr. Barrett makes the suggestion 
that the traces of oil, or other organic matters which 
find their way into a steam-boiler, may similarly pro- 
duce a sudden generation of steam sufficient to account 
for certain problematical explosions, and thus lends some 
strong confirmatory evidence to the idea often promul- 
gated by others within and without the engineering 
profession. 

21. Steady Rise in Pressure has been shown by 
the experiments of the committee of the Franklin Insti- 
tute and by numerous cases of explosion, both before 
and since their time, to be capable of producing very 
violent explosions. In such cases, the steam being 
formed more rapidly than it is given exit, the pressure 
steadily increases until a limit is found in the final rup- 
ture of the weakest part of the boiler. Should this 
break occur below the water-line and be the result of 
local decay or injury, no explosion may ensue; but 
should the rupture be extensive, or should it occur 
above or near the surface of the water, the succession of 
phenomena described by Clark and Colburn may follow, 
and an explosion of greater or less violence may take 
place. The intensity of the effect will depend largely 
upon the quantity of stored energy liberated, and partly 
upon the suddenness with which it is set free. A slowly 
ripping seam, or gradually extending crack, would per- 
mit a far less serious effect than the general shattering 
of the shell, or an instantaneously produced and exten- 
sive rent. 



STEADY RISE IN PRESSURE, 



95 



The time required to produce a dangerous pressure is 
easily calculated when the weight of water present, W y 
the range of temperature above the working pressure 
and temperature, t\ — /2> and the quantity of heat, Q t 
supplied from the furnace are known, and is 

T _W{tf—tj) , 

Q J 

Professor Trowbridge gives the following as fair illus- 
rations of such cases : # 

(i.) A marine tubular boiler of largest size, such that 

w=79,ooo lbs. of water. 

Suppose the working pressure to be 2*^, and the 
dangerous pressure 4 atmospheres. 

The boiler contains 6,000 square feet of heating sur- 
face; and supposing the evaporation to be 3 lbs. of 
water per hour for each square foot, we shall have, tak- 
ing 1,000 units of heat as the thermal equivalent of the 
evaporation of I lb. of water, 



Q= 



ti-t=29° R 
5000X3X1000 



60 



_ 7900x29 

j>__/ =9.1 minutes. 

5000X3x1000 * 

60 



9 6 STEAM BOILER EXPLOSIONS. 

(2.) A locomotive boiler, containing 5,000 lbs. of 
water, having 1 1 square feet of grate-surface, and burn- 
ing 60 lbs. of coal per hour on each square foot of grate, 
each pound of coal evaporates about 7 lbs. of water 
per hour, making 77 3bs. of water evaporated per 
minute. 

Suppose the working pressure to be 90 lbs. and the 
dangerous pressure to be 175 ; 

h— t=$o° F. 

rr 5000X50 _y . , 

T=- £__ = 3% minutes. 

77X1000 

(3.) The Steam Fire-Engine, — The boiler contains 
338 lbs. of water and 157 square feet of heating-sur- 
face. Supposing each square foot of heating-surface to 
generate 1 ib. of steam in one hour, the pressure will 
rise from 100 to 200 fbs. in 

T=y minutes. 

(4.) To find, in the same boiler, how long a time 
will be required to get up steam ; that is, to carry the 
pressure to 100 lbs. If we suppose but \}4, cubic feet 
of water in the boiler, we shall have 

_ 93X117 

7==—^ — ' =4. 1 minutes. 
157X 1000 

" ~6cT 
Thus, if w is diminished, the time t is diminished in the 



STEADY RISE IN PRESSURE. 



97 



same proportion. The lowering of the water-level from 
failure of the feed-apparatus increases the danger, not 
only by exposing plates to overheating, but by causing 
a more rapid rise of pressure for a given rate of com- 
bustion. Gradual increase of pressure can never take 
place if the safety-valve is in good order, and if it have 
sufficient area. 

The sticking of the safety-valve, either of its stem 
or to its seat, the bending of the stem, or the jamming of 
the valve by a superincumbent object or lateral strain, 
and similar accidents, have produced, where boilers were 
strong and otherwise in good order, some of the most 
terrific explosions of which we have records. The parts 
of the boiler have been thrown enormous distances, and 
surrounding buildings and other objects levelled to the 
ground; while the report has been heard miles away 
from the scene of the disaster. 

The records of the Hartford company, up to 1887, 
include accounts of 26 explosions of vessels detached 
from the generating boiler, used at moderate pressures, 
for various purposes in the arts, and there have been 
many others of less importance that were not consid- 
ered worthy of public mention. It is concluded that 
the percentage of explosions among bleaching, digest- 
ing, rendering, and other similar apparatus is ten times 
greater than among steam-boilers at like average press- 
ures, and the destructive work done is quite as astonish- 
ing as that by the explosion of ordinary steam genera- 
tors. * 

% The Locomotive, 1887. 



98 STEAM BOILER EXPLOSIONS. 

This is sufficiently decisive of the question whether it 
is possible to produce destructive explosions simply by 
excess of pressure above that which the vessel is strong 
enough to withstand. In these cases, low-water, and 
all the other special causes operating where fire and high 
temperature exist, and such absurd theories as the gen- 
eration of gas, or the action of electricity, are elimi- 
nated, and it is seen that mere deterioration and loss of 
strength, or a rise of steam-pressure, even where there 
is an ample supply of water, may produce explosions of 
the utmost violence. 

22. The Relative Safety of Boilers of the various 
types, is determined, mainly, by their general design 
and their greater or less liability to serious and exten- 
sive injury by the various accidents and methods of de- 
terioration to which all are to a greater or less extent 
liable. The two essential principles by which to com- 
pare and to judge the safety of boilers, are : 

(i). Steam-boilers should be so designed, con- 
structed, operated, inspected and preserved, as not to be 
liable to explosion. 

(2). Boilers should be so designed and constructed 
that, if explosive rupture occurs at all, it shall be with 
a minimum of danger to attendants and surround- 
ing objects. 

The prevention of liability to explosion and the pro- 
vision against danger should explosion actually take 
place, are the two directions in which to look for 
safety. 

As Fairbairn has remarked, the danger does not con- 



THE RELATIVE SAFETY OF BOILERS. 99 

sist in the intensity of the pressure, but in the character 
and construction of the boiler.* Other things being 
equal, that boiler, or that form of boiler, in which the 
original surplus strength of form and detail is greatest, 
and which is at the same time best preserved, is the 
safest. That class in which original strength is most 
certainly and easily preserved, has an important advan- 
tage ; those boilers in which facilities for constant over- 
sight, inspection and repairs are best given, are superior 
in a very important respect to others deficient in those 
points. For example, the cylindrical tubular boiler, if 
properly set, is very accessible in all parts, and may be 
at all times examined ; it offers peculiar facilities for in- 
spection and the hammer-test, and can be readily kept 
in repair ; but it is liable, in case of its becoming weak- 
ened by corrosion over any considerable area, or along 
any extended line of lap, to complete disruptive explo- 
sion. 

On the other hand, the various u sectional," or so- 
called " safety" boilers, are rarely as convenient of ac- 
cess or of inspection, and cannot usually be as readily 
and completely cleaned ; but they are so designed and 
constructed as to be little, if at all, liable to dangerous 
explosive rupture, and if a tube or other part bursts, it 
is not likely to endanger life or property. That boiler 
is, therefore, on the whole, best which is least liable to 
those kinds of injury which lead to explosion, and which 
is least likely to do serious harm should explosion actu- 

*Engineering Facts and Figures, 1865. 



ioo STEAM BOILER EXPLOSIONS. 

ally take place. # Those who select the tubular boiler 
are commonly influenced mainly by considerations of 
cost, and the first of the above considerations ; while 
the users of the water-tube sectional boilers are con- 
trolled by the second, so far as either considers this 
form of risk at all. 

During the experiments of Jacob Perkins, about 1825 
and later, the value of the " sectional " boilers, where 
high pressures are adopted, was well shown. He fre- 
quently raised his steam-pressure to one hundred atmos- 
pheres,! and in his earlier work rupture often took place, 
but no ill effects followed. The division of the boiler 
into numerous compartments saved the attendants from 
injury. In a letter to Dr. T. P. Jones, dated March 8. 
1827,$ Mr. Perkins states that he had worked at the 
above-mentioned pressure, with a ratio of expansion of 
12; his usual pressure was about two-thirds that 
amount, and the ratio of expansion 8. Mr. Perkins 
was then building an engine to safely carry a pressure 
of 2,000 pounds per square inch.^ 

23. Defective Designs, causing explosion, are not 
as common as many other causes. They exist, how- 
ever, more frequently than is probably usually supposed. 
The de'ects are generally to be observed in the staying 

*Dr. E. Alban, following John Stevens, was probably the first to en- 
nunciate the principle : " So construct the boiler that its explosion may 
not be dangerous." The High-Pressure Steam-Engine, 1847, p. 7°- 

f Jour. Franklin Institute, Vol. 3; p. 415. 

% Ibid, p. 412. 

§ Reports on Steam Boilers, H. R., 1832, p. 188. 



DEFECTIVE DESIGXS. 101 

of such boilers as require bracing; in the insertion of 
the heads of plain cylindrical boilers ; in the attachment 
of drums and the arrangement of man-holes and hand- 
holes, and, less frequently, in the selection of the proper 
thickness and quality of iron for the shells and flues. 
Such defects as these are the most serious possible ; 
they are not only serious in themselves, and at the start, 
but are of a kind which is commonly very certain to be 
exaggerated and rendered continually more dangerous 
with age. A thin shell grows constantly thinner, a 
weak stay or brace weaker, and an unstayed head more 
likely to yield every day ; while a flue originally 
too thin is all the time overstrained, not simply by the 
steam-pressure, but also by the action of the relatively 
stronger parts around it. The most minute study of 
every detail, and the most careful calculation of the 
strength of every part, with an allowance of an ample 
factor of safety, are the essentials to safety in design. 

Faulty design in bracing is illustrated by an explo- 
sion which took place in New York City, January 15 th,* 
188 1, by which, fortunately, however, no loss of life was 
caused. A dome-head, proportioned and braced as 
shown in the next figure, was blown out, and tore up a 
side-walk under which the boiler was set, doing no 
other damage. The case was reported on by Mr. Rose, 
substantially as follows : 

" The dome-crown, tearing around the edge, at A, also 
tore across at B, being thus completely severed. The 
iron at the fractures was of excellent quality. The plate 



102 



STEAM BOILER EXPLOSIONS. 



showed lamination in places, and the crack around A 
was rusty and evidently not of recent formation. 

The six stays, three of which are shown in place at C, 
Fig. 13, were all in position in the dome, and their sur- 




Fig. 13. — Dome and Head. 



faces of contact with the dome were covered by a black 
polish indicating movement and abrasion. 



ill 

m 
m 






_^ 


^^^B 




__^=t 


^^^^r^ ^—d 


















1 


IrJfilBiS 


w 




... 


ML 


,l^^^^^fe; 


§m 


^finfflrn) 3 ° ° ° P im WwSb^ 




31 



Fig. 14. — Explosion of Dome. 

Apparently, as the pressure and temperature increased 
and decreased the dome-head might lift and fall, bend- 



DEFECTIVE DESIGNS. 



103 



ing on A as a center. Thus taking I as a center, the 
movement of C would be in the direction of F, while at 
D the direction would be toward J, and the direction of 
motion of the two would nearly coincide. 

The exploded dome shows an indentation at I, due to 
the motion of the foot of the stay. 

Another error in the design of this boiler is that the 
diameter of the dome shell is 34 inches, and a circle of 
iron about 18 inches in diameter is punched out of the 




Fig. 15. — Defective Form. 

shell at D. This opening is required only to admit an 
inspector or workman to the interior of the boiler, hence 
it is several inches wider than it should be. 

Defective design is illustrated in the case of the boiler, 



104 STEAM BOILER EXPLOSIONS. 

the explosion of which left it in the form shown in the 
engraving.* 

This boiler consisted of two incompletely cylindrical 
shells, united as in the next figure, and ineffectively 



Fig. 16. — Junction of Shells. 

stayed at the lines of contact This is a form which, 
insufficiently braced, becomes peculiarly dangerous. 
In the case illustrated, the braces yielded, after having 
been weakened by continual alteration of form, and 
split the two shells apart as seen. It is probably possible 
to brace boilers of this type safely, but it is safer to 
avoid their use. They have sometimes been used for 
marine purposes, where lack of space compelled special 
expedients, the bracing consisting of strong bolts with 
nuts and washers on the outside of the shell; a compar- 
atively strong and safe construction. 

Steam-domes are a source of some danger and of ad- 
ditional expense, however well designed and attached, 
and it is probably good economy, all things considered, 
to dispense with them altogether, using a dry-pipe, in- 
stead, and expending the amount of their entire cost on 
an increase in size of boiler over that which would have 
otherwise been selected. The large boiler will steam 
easier and more regularly, will give dryer steam, and 
will be less liable to dangers of deterioration or of ex- 

* Locomotive Feb., 1880. 



DEFECTIVE DESIGNS. 105 

plosion. A steam-drum above the boiler and connect- 
ed by two separate nozzles, or a drum connecting the 
several boilers of a battery is not subject to the objec- 
tions which apply to the attached dome. 

24. Defective Construction, material and work- 
manship are responsible for many explosions of steam- 
boilers. 

Thin, laminated, or blistered sheets, imperfect welds 
in bracing, the strains produced by the drift-pin, care- 
lessness in the attachment of nozzles and drums, and in 
neglect of the precaution of straightening man-holes 
and hand-holes, and bad riveting, are all common 
causes of weakness and accidents. Only the most 
careful and skillful, as well as conscientious builders, 
can be relied upon to avoid all such faults, and to turn 
out boilers as strong and safe as the designs may per- 
mit. In all cases, careful and unintermitted inspection 
by an experienced, competent and trustworthy inspec- 
tor, should be provided for by the proposing purchaser 
and user of the boiler. In the case of some of the more 
modern forms of boiler, constructed under a system of 
manufacture which includes some machine fitting and 
working to gauge of interchangeable parts, with regular 
inspection before assemblage, this supervision becomes 
less essential, and a careful test and trial previous to ac- 
ceptance, may be all that is necessary to insure a satisfac - 
tory and safe construction. Whenever defective material 
or bad workmanship is detected, the fault should always 
be corrected before the boiler is accepted, and previous to 
any trial or use under steam. Careless riveting and the 



io6 



STEAM BOILER EXPLOSION^. 



use of the drift-pin are defects which cannot often be 
readily detected afterward, and they are such common 
causes of explosion that too much care cannot be taken 
to avoid any establishment of which the reputation, in 
this regard, is not the best 

Defective welds, the cause of many unfortunate acci- 
dents following the yielding stays or braces, are among 
the most common and least easily detected of all faults. 
They are due to the difficulty of producing metallic con- 





Fig. 17. — Defective Welding. 

tact in abutting surfaces between which particles of 
scale and superficial oxidation may interpose. The 
grain of the iron, as illustrated in the accompanying 
engraving, is broken at such junctions, and it is difficult to 
secure a good weld, and next to impossible to determine 
until it actually breaks, whether it is seriously unsound. 
Defective workmanship is often exhibited most strik- 
ingly by the distorted forms of rivets, revealed after ex- 
plosion has caused a fracture along the seams, or when 
the yielding of the weakened seam has resulted in an 



DEFECTIVE CONSTRUCTION. 



107 



explosion. The following illustrations of a variety of 
cases of such distortion, all taken from a single boiler,* 
show how very serious this kind of defect may be. It 
is not to be presumed that such carelessness, or worse, 
as is here exemplified, is to be attributed to the builder 
himself, but rather to the fault of the workmen care- 
fully concealing their action from the eye of the foreman 
or inspector. No law or rule can protect the purchaser 
from this kind of fault; his only reliance must be upon 
the reputation of the maker and his workmen, and the 
vigilance and skill of his inspector. 

Fig. 18. — Rivet " driven " in over-set 
holes, the conical point broken off by the 
tearing apart of the plates, the head nearly 
severed from the body, and probably 
weakened in driving. 

FlG. 19.— Rivet "driven" 
in over-set Iroles, heads bro- 
ken off by the tearing apart of the plates, 
conical point also nearly broken off, bad 
sample of " driving," cone too flat to pro- 
perly hold down the plate. FlG - x 9« 

The next figure illustrates a group of similar distorted 
rivets which played their part in the production of an 
explosion. 




Fig. 18. 




* Locomotive, Feb., 1880. 



ioS 



STEAM BOILER EXPLOSIONS. 




Fig. 20. — Defective Rivets. 
Fig. 21. — Rivet " driven " in slightly 
over-set holes, point eccentric and not 
symmetrical, too flat to properly secure 
the edge of the plate. 

FlG. 22: — Rivet " driven " in 

badly over-set holes, very 

FlG ' 2I * weak. See Figs. 23, 24 and 

25, which were " sheared " at the time of the 

explosion. The dark shading on lower 

end Fig. 22 indicates an old crack. 

Figs. 23, 24, 25. — Samples selected from a number 
taken from a " sheared " seam, which was believed to be 








Fig. 22. 




Fig. 23. Fig. 24. Fig. 25. 

the initial break from which the explosion arose. They 
were no doubt similar to Fig. 22 before they gave way. 



DEFECTIVE C0NSTRUCT10X. 



109 



The Author, on one occasion, picked out with his 
fingers twelve consecutive rivets, deformed like those 
here illustrated, from a torn seam in an exploded boiler. 
FlG. 26. — Rivet ''driven" in over-set 
holes ; it was probably fractured under 
the head in driving. Taken from a seam 
that was broken through the rivet holes. 

FlGS. 27 and 28. — Long rivets taken 
from a broken casting which they were in- 
tended to secure to the wrought-iron head 
of the boiler. The holes in the wrought-iron plate 
were " drifted " and chipped to allow the rivets to en- 
ter, as shown by the enlarged portion of the body. 




Fig. 26. 





Fig. 27. 



Fig. 28. 



This irregular upsetting and the sharp little wave of iron 
on the body of Fig. 27 indicate the thickness of the 
wrought-iron plate. 



HO STEAM BOILER EXPLOSIONS. 

25. Developed Weakness, usually a consequence 
of progressing decay by corrosion, is the most common 
of all causes of the explosion of steam-boilers. A 
boiler, designed and constructed of the best possible pro- 
portions and of the best of materials, having at the 
start a real factor of safety of six, may be assumed to 
be as safe against this kind of accident as possible ; but, 
with the beginning of its life, decay also begins, and the 
original margin of safety is continually lessened by a 
never ceasing decay. The result is an early reduction 
of this margin to that represented by the difference 
between the working-pressure and that fixed as a max- 
imum by the inspector's tests. Should this difference 
be sufficient to insure against accident, resulting from 
further depreciation, in the interval between inspector's 
or other tests, explosion will not occur; should this 
margin not be sufficient, danger is always to be appre- 
hended, and, almost a certainty that rupture, and possibly 
explosive rupture, will at some time occidr. The mar- 
gin is legally, usually fifty per cent; it is too small to 
permit the proprietor to feel a real security. It is 
usually thought that the tests should show soundness 
under pressure, at least at double the regular working- 
pressure at which the safety-valve is set* Many cases 
have been known in which the boiler has yielded at the 

^Experiments made by the Author, and later, by other investigators, 
have indicated the possibility that an apparent factor of safety of two, un- 
der load momentarily sustained, may not actually mean a factor exceeding- 
one for permanent loading. Materials of Engineering, Vol. I., §133; 
Vol. II., §295. 






DE VEL OPED WE A KNE SS. 



working-pressure not very long after the regular official 
inspection had taken place. 

Such an example was that of the explosion of the 
boiler of the "Westfield," in New York harbor, in June, 
1876. The steam ferry-boat " Westfield," is one of three 
boats which have formed one of the regular lines between 
New York and Staten Island. The " Westfield " made 
her noon trip up from the Island to the city, on Sunday, 
July 30th, and while lying in the New York slip, her 
boiler exploded, causing the death of about one hun- 
dred persons and the wounding of as many more. 

The boiler is of a very usual form, as represented in 
Fig. 29, and is known as a " Marine return-flue boiler." 
The diameter of its shell- — the cylindrical part was rup- 
tured — is ten feet : its thickness, No. 2 iron, twenty- 
eight hundredths of an inch. 




Fig. 29. — Boiler of the Westfield. 

The evidence indicated that the explosion occurred 
in consequence of the existing of lines of channeling and 
long existing cracks, by which the boiler was gradually 



H2 STEAM BOILER EXPLOSIONS. 

so weakened, that, six weeks after its inspection and 
test, the pressure of steam being allowed by the engineer 
to rise slightly above the pressure allowed, the boiler 
was ruptured, giving way along a horizontal seam 
and tearing a course out of the boiler. 

The common lap-joint, customarily adopted in the 
construction of boilers, is liable to such serious distortion 
under very heavy pressure, as to produce leakage be- 
fore actually yielding, and this leakage is sometimes so 
great as to act as a safety-valve. Thus, suppose a 
straight strip of plate riveted up in parts as in Fig. 30.* 
A heavy pull will cause distortion as shown, in all cases 
except where a butt-joint is made with a covering string 
on each side. If the metal is brittle, and the rivet-heads 
strong, preventing the bending of the plate on the line 
of rivet-holes, the plate will probably break adjacent to 
G or F, Fig. 30; or in the middle, I and H. But should 
the plates be ductile or the rivet-heads weak, the break 
would occur at the line through the holes. 




Fig. 30. — Yielding Joints. 

If the plates, Fig. 30, A, etc., were straight at the 
joint, the extreme end, L, must contract and the outer 
one expand at M, involving in the one a compression or 
upsetting, and in the other drawing the metal. If the 

* See Locomotive, Oct., 1880. 



DEVELOPED WEAKNESS. 



113 



joint be a butt, with a single outer cover, C, a similar 
contraction must take place at both ends and a con- 
traction of the middle of the covering strip, while the 
opposite would take place in the case of the joint with 
the inner cover, B ; these distortions are not likely to 
take place in a transverse seam of a cylindrical boiler 
shell from internal pressure. The butt-joint, with two 
covering-plates, E, would retain its shape. 

The next Figures, 31, 35, show the effect of strain on 
rivet-holes, and on holes filled by the rivet. Lapped 



n 



s 



3 



1 

( 


) 


H 




K 


J V, 






r 


"\ 


> 




k. 


J 






( 


^ 1 






c 


) 






F 


I 







H 

If 

3 L 



Fig. 31. Before Stretching. Fig. 32. After Stretching. 

longitudinal joints are shown at A', Fig. 30. Single- 
riveted and single-covered butts at B' and C. D' shows 
a double-riveted single-covered butt. 

Multiple Explosions are not infrequent. They 
usually occur in consequence of the explosion of one of 
a battery, with the result of injuring adjacent boilers in 
such a manner that they explode, the phenomena fol- 
lowing each other so quickly, as to produce the appear- 
ance of simultaneous explosion. It is possible, also, 
that, in some cases, an accession of pressure in a 
set of boilers, may take place with such suddenness as 
to explode several, notwithstanding there may exist a 
difference in their resisting power ; the weakest not be- 



1 14 STEAM BOILER EXPLOSIONS. 

ing given time to act as a safety valve to the rest. It is 
doubtful, however, whether such cases can often, if ever, 
arise. 

26. General and Local Decay introduces vastly 
different degrees and elements of danger. As has been 
elsewhere stated, in effect, an explosion comes of extend- 
ed rupture; while local injuries or breaks, if they do not 
lead to wider injury, cannot cause widespread disaster. 
Hence, general corrosion, extending over considerable 
areas of plate, or along lines of considerable length, is a 
cause of danger of complete disruption and explosion. 
A corroded spot in a fire-box, a loosened rivet, or even 
a broken stay, if the boiler be otherwise well-propor- 
tioned, well-built, and in good order, may not be a 
serious matter, but a thinned sheet in the shell, a long 
groove under a lap, a line of loose rivets, or a cluster of 
weakened stays or braces, will certainly be most dan- 
gerous. General or widespread corrosion is very 
liable to lead to explosion; local and well-guarded cor- 
rosion may cut quite through the metal and simply 
cause a leak or an unimportant " burst." Old fire- 
boxes are often seen covered with "patches" in places, 
and yet they very rarely explode. Such a state of af- 
fairs may, nevertheless, by finally producing large areas 
of patched and fairly uniformly weak portions of the 
boiler, lead to precisely the conditions most favorable 
to explosion. A steam-boiler experimentally exploded 
at Sandy Hook, N. J., Sept., 187 1,* had previously, by 

* Journal Franklin Institute, Jan., 1872. 



GENERAL AND LOCAL DEC A Y. 



"S 



repeated rupture, by hydraulic pressure and patching, 
been gradually brought into precisely this state, and ex- 
ploded under steam at 53^ pounds, about four atmos- 
pheres pressure, a slightly lower pressure than it had 
sustained (59 pounds) at its last test. On this occasion, 
when a pressure was reached of 50 pounds per square 
inch, a report was heard which was probably caused by 
the breaking of one or more braces, and at 5 3 y 2 pounds, 
the boiler was seen to explode with terrible force. The 
whole of the enclosure was obscured by the vast masses 
of steam liberated; the air was dotted with the flying 
fragments, the largest of which — the steam drum — rising 
first to a height variously estimated at from 200 to 400 
feet, fell at a distance of about 450 feet from its original 
position. The sound of the explosion resembled the re- 
port of a heavy cannon. The boiler was torn into many 
pieces, and comparatively few fell back upon their origi- 
nal position. 




Fig. 33. — Corrosion. 

Thus corrosion may affect a single spot in a boiler, in 
which case a " patch," if properly applied, Should make 



Il6 STEAM BOILER EXPLOSIONS. 

the boiler nearly as strong as when whole. A series of 
weak spots near each other may so weaken a boiler as 
to produce explosion, as may any considerable area of 
thin plate, although, when occuring in the stayed sur- 
faces of a fire-box, the metal may become astonishingly 
thin. A sketch of spots of corrosion is shown in Fig. 
33, which represents the cause of an actual explosion. 
This cause of explosion may be either internal or exter- 
nal, and is produced internally by bad feed-water, and 
externally by dampness or by water leaking from the 
boiler, either unseen or neglected. It is always dan- 
gerous to have any portion of a boiler concealed from 
observation. 

The effect of covering a part of a sheet subject to cor- 
rosion by solid iron, as by the lap of a seam, is shown in 
the next figure, which also exhibits a common method 




Fig. 34. — Corrosion at a Seam. 

of corrosion along a seam. The same effect is seen still 
more plainly in the succeeding figure, in which the pit- 
ting which so often attends the use of the surface con- 
denser is also well shown. 



THE METHODS OF DECAY. 



117 




Fig. 35. — Pitting. 

27. The Methods of Decay are as various as the 
forms and locations of the parts subject to corrosion. 
As Colburn* has said " As a malady, corrosion corres- 
ponds in its comparative frequency and fatality, to that 
great destroyer of human life, consumption/' and it has 
as innumerable phases and periods of action. The two 
most common methods of decay are the general, and 
here and there localized, corrosion, that goes on in all 
boilers, and, in fact, on all iron exposed to air and car- 
bonic acid presence of moisture ; and the concentrated 
and localized oxidation that is often seen along the line 
of a seam, at the edge of the lap, where the continual 
changing of form of the boiler is as constantly producing 
an alternate flexing and reflex motion of the sheet which 
throws off the oxide as fast as formed along that line, 
and exposes fresh, clean metal to the corroding influence. 



'Trans. Brit. Assoc, 1884. 



Il8 STEAM BOILER EXPLOSIONS. 

A groove or furrow is thus, in time, produced, which 
may, as occurred in the case of the " Westfield," Fig. 
36, actually cut through the sheet before explosion 
takes place. 

The phenomenon known as " grooving " or " furrow- 
ing" is well illustrated by the case just mentioned, in 
which this action was originally started, probably by 
the carelessness of the workman, who, either in chipping 
the edge of the lap along a girth seam, or in caulking 
the seam, scored the under sheet along the edge of the 
lap with the corner of his chisel, or with the caulking- 
tool. This is a very common cause of such a defect. 

The boiler was broken into three parts. The first, and 
by far the largest part, consisted of the furnaces, steam- 
chimney and flues, with a single course of the shell ; the 
second consisted of two courses of the outside shell next 
the back head, together with that head, to which they 
remained attached ; the third piece consisted of a single 
complete course from the middle of the cylindrical shell, 
which was separated at one of its longitudinal seams, 
partially straightened out and flung against the bottom 
and side of the boat. The last piece remained opposite 
its original position in the boiler, before the explosion, 
while the first and second pieces went in opposite direc- 
tions, the former finally lying several feet nearer the en- 
gine than when in situ, and against the timbers of the 
" gallows-frame/' while the latter piece was thrown fifty 
feet forward into the bow of the boat, where it fell, torn 
and distorted. The longitudinal seam, along which 
piece number three separated, and the deep score or 



THE METHODS OF DECAY, 



119 



"channel " cutting nearly through in many places, and 
presenting every evidence of being an old flaw, were 
plainly seen. The mark made by a chisel in chipping, 
and that of the caulking-tool, were seen, and indicated 
the probable initiative cause of the flaw. 

The Author examined this piece and found an old 
crack or " channel" cut, along the edge of 'Jre horizon- 
tal lap referred to as being at the ends of the sheet, and 
in some places so nearly through that it was difficult to 
detect the mere scale of good iron left, while in other 
places there remained a sixteenth of an inch of sound 
metal. Fig. 36 exhibits a section of the 
crack. 

Were this the weakest part in the 
boiler, and the least thickness here one- 
sixteenth of an inch, the tensile strength 
being equal to the average determined 
by the tests to be described, the pressure 
required to rupture such a boiler, ten 
feet in diameter, would be 44079X1-16 
X 2-7- 1 20=47 lb s - P er square inch, near- 
ly. A pressure of twenty-seven pounds 
would burst it open where the least thick- 
ness was slightly more than one-thirty-second of an inch. 
One portion may be supported, to some extent, by a 
neighboring stronger part. Along this longitudinal 
seam the limit of strength would seem to have been 
about thirty pounds per square inch, which is about the 
pressure at which the boiler exploded, this seam ripping 
for a distance of several feet. 




Fig. 36. 

Grooving. 



120 STEAM BOILER EXPLOSIONS. 

The original strength of the boiler was equal to about 
one hundred and twenty pounds along the horizontal 
seams — its then weakened parts, — provided that the 
iron had, when new, the average strength of the speci- 
mens which we have tested. In the vertical seams may 
be seen, in some places, similarly weakened portions, 
the cracks running usually from rivet to rivet, and here 
and there exhibiting marks that show the wedging 
action of the " drift-pin/' and many places, both in 
longitudinal and girth seams, are cut by the chisel and 
marked by the "caulking- tool." 

These lines of " furrowing " are sometimes continuous, 
and sometimes interrupted by portions of good iron. 
They are probably, in most cases, caused by changes in 
form of the boiler with variations of temperature and 
pressure, some line of local weakness determining the 
line along which the plate shall bend; and this bending 
taking place continually, though ever so slightly, along 
the same line precisely, finally produces rupture. This 
change of form of the shell of a boiler may be due to 
either the constantly occurring variation of pressures, as 
steam is made or is blown off, during working hours ; or 
it may be produced by changes of temperature. Large 
and thin boilers are especially liable to this form of in- 
jury. Bad methods of support may permit, or may 
cause variations of form and defect; which is all the 
more dangerous that it is difficult, in many cases, to de- 
tect it. Water trickling from cracks sometimes causes 
a kind of grooving along its path, often hardly less 
serious in its nature and extent. 



THE METHODS OF DECAY. 121 

Sometimes this action produces a narrow crack, and 
at other times, as above stated, as the rust formed is 
thrown or scoured off the iron at the bend, leaving a 
comparatively clean surface, oxidation is probably accel- 
erated, and the fault takes the form of a groove or fur- 
row. If unperceived, this goes on until a rupture or an 
explosion occurs. 

Of forty explosions of locomotive boilers noted in 
British Board of Trade reports,* eighteen gave way at 
the fire-box and twenty at the barrel. Of these twenty, 
every one was the result of " grooving " or cracks along 
the lap of seams, all of which were lap-joints. The 
grooves were most common ; they always occurred 
along the edge of the inside over-lap, just where the 
changes of form with varying pressure would concen- 
trate their effects. Such results are sometimes also 
seen at butt-joints, especially where a strip has been 
used inside. The racking action of the engines may 
produce precisely the same effect. Wherever change 
of form is felt, grooving or furrowing, and cracking, may 
be expected to be found in time. Where the boiler is 
already heavily strained along one of these lines of re- 
duced thickness, any slight added stress, as ajar, or the 
action of a caulking- tool, as where leaks in boilers under 
pressure are being caulked, may precipitate an explo- 
sion, the break following the groove or crack just as a 
stretched drum-head may yield to the scratch of a 
knife. 

s 

* Wear and Tear of Steam Boilers ; F. A. Paget, Trans. Soc. of Arts, 
1865. London, 1865, p. 8. 



122 STEAM BOILER EXPLOSIONS. 

28. Differences in Temperature between parts of 
a boiler more or less closely connected in the structure 
may produce serious strains, and some instances of explo- 
sion have been attributed to this cause. 

Changes of temperature ©ccur as steam is raised or 
blown ofif from a boiler, and its temperature at one time 
becomes that due the steam-pressure, and then it falls 
to that of the atmosphere each time that steam is blown 
off. It will change its form more or less, and will usually 
be subjected to some strain by this process. Again, 
while actually at work, the steam-space and upper por- 
tion of the water-space are at the temperature of steam 
at the working-pressure, while the lower part is contin- 
ually varying in temperature from that of the feed- 
water to the maximum which it attains after entrance. 
This difference of temperature between the upper and 
lower parts of the boiler, as well as between other por- 
tions, causes a continual tendency to distortion, and, if 
this distortion be resisted, a stress is thrown upon the 
parts equal to that which would be required, acting 
externally, to remove the distortion, if produced. The 
stress is also equal to the mechanical force that would be 
necessary to produce similar distortion. 

Thus, had the temperature of the main and upper 
part of the " Westfield's " boiler been, after the entrance 
of the feed-water, 273 , or that due to about twenty- 
seven or twenty-eight pounds steam, while the feed- 
water having a temperature of 73 °, the bottom of the 
boiler having a temperature, in consequence, 200 below 
that of the top, the difference in length would b^ about 



DIFFERENCES IN TEMPERATURE. 



123 



one-eight-hundredth, and, if confined by rigid abut- 
ments, iron so situated would be subject to a stress of 
twelve and a half tons per square inch. But, in this 
case, one part would yield by compression and the other 
by extension, and if they were to yield equally it would 
reduce the stress to six and a quarter tons. Actually, 
in this case, the lower fourth and upper three-fourths 
would be likely to act against ^ach other, and the stress, 
if the boiler had no elasticity of form, would be about 
nine tons. Any elasticity of form — and boilers gener- 
ally possess considerable—would still further reduce the 
strain, and it very frequently makes it insignificant. 

It is thought, by more experienced engineers and 
other authorities, that many of the explosions known to 
have taken place, after inspection and test, at pressures 
lower than those of the test, are caused by the weaken- 
ening action of unequal expansion, the stresses and 
strains produced in this manner being superadded to 
those due to simple pressure, against w r hich latter the 
boiler might otherwise have been safe. Such defects 
may also be the final provocation to explosion when 
cold feed- water is pumped into a boiler, on getting up 
steam, or possibly, sometimes, when cooling off. It has 
even been asserted that an empty boiler has been rup- 
tured by such changes of form consequent on building 
a light fire of shavings in a flue to start the scale. The 
Author has known of instances in which the girth-seams 
of large new marine flue-boilers were ruptured along the 
line of rivet-holes a distance of several feet by the intro- 



I2 4 



STEAM BOILER EXPLOSIONS. 



duction of a large volume of cold feed-water, when 
steam was up, but the engine at rest. 

The differences of temperature on the two sides of the 
sheet may be important. While it is true that the heat 
supplied by the furnace-gases is absorbed by the boiler 
to the same extent, practically, without much regard to 
the thickness of the plates of the boiler, it is a well- 
known fact that the resistance of iron to the flow of heat 
is so great that the effect of heat on the metal itself is 
seriously modified by the thickness of the sheet. Heavy 
plates " burn " away, projecting rivet-heads are de- 
stroyed and the laps of heavy plates are especially liable 
to be thinned seriously where they are employed. 

A variation of temperature of considerable range, and 
often recurring, frequently causes injury by hardening 
the metal of the boiler, making it brittle and liable to 
crack with change of form, and also produces the very 
change of form causing this cracking. The experiments 
of Lt.-Col. Clark, R. A.,* show that great distortion 
may be thus produced. It is probably thus that iron, 
and especially steel, fire-boxes so often crack, in conse- 
quence of a continual swelling of the metal under vary- 
ing temperatures and the stresses so caused. This 
action, combined with oxidation, external and internal, 
sometimes makes the plates, and often the stays, of the 
boiler remarkably weak and brittle ; they sometimes 
become more like cast than wrought-iron. The thicker 
the sheet, the more readily is it overheated and over- 
strained. 



Proc. Royal Society, 1863 ; Jour. Franklin Inst., 1863. 



THE MANAGEMENT OF THE STEAM-BOILER. 125 

The extent to which alteration of form under pressure 
may go, with good material before actual rupture, is 
illustrated by the following:* 

During the summer of 1868 a cylindrical boiler, made 
of y£ inch steel plates, built at the Fort Pitt Iron Works, 
Pittsburgh, was tested under authority of the govern- 
ment, with a view to determining the relative advantages 
of steel and iron as a material for navy boilers. When 
the pressure of cold water had reached 780 lbs., the 
"girt" of the boiler was found to have permanently 
increased 3^ inches, and at 820 lbs., rupture occurred. 

Cases have been known in which a steel crown-sheet 
has become overheated, and has sagged down until, the 
tube-sheet going with it, a basin-shaped form has been 
produced, convex toward the fire, and yet no fracture 
produced, even when the pump w r as put on and the 
boiler filled up again under pressure. 

29. The Management of the Steam-Boiler, or, 
more correctly, its mismanagement, while in operation, 
and a neglect of proper supervision and inspection, may 
be considered, on the whole, the usual reason of explo- 
sion, as the deterioration of the boiler is the immediate 
cause, and this deterioration is almost invariably so 
gradual and so readily detected by intelligent and pains- 
taking examinations that there is rarely any excuse for 
its resulting disastrously. A well-made boiler, under 
good management and proper supervision, may be con- 
sidered as practically free from danger. 

* Iron Age, Sept. 26, 1872. 



j 26 STEAM BOILER EXPLOSIONS. 

The person in direct charge of the boiler is usually 
a presumably experienced and trustworthy man. He 
should be thoroughly familiar with his business, gener- 
ally intelligent, of good judgment, ready and prompt in 
emergencies, and absolutely reliable at all times. His 
first duty is to see that the boiler is full to the water- 
line, trusting only the gauge-cocks ; he must keep con- 
stant watch of the furnaces, flues and other surfaces sub- 
ject to the action of the fire, and thus be certain that no 
injury is being done by overheating or sediment; he 
must keep the feed-apparatus in perfect working order, 
keep up the supply of water continuously and regularly, 
and see that the safety-valve is in good order at all times. 
Such careful management, conscientious inspection and 
cleaning, and repairing at proper intervals, will insure 
safety. 

To keep the safety-valve in good working order and 
to make certain that it is operative, provision should be 
made for opening it by hand, and it should be daily 
raised, before getting up steam, to the full height of its 
maximum lift. 

Explosions of gas sometimes precipitate steam-boiler 
explosions. Should the gases leaving the fuel and the 
furnace not be completely burned, but become so min- 
gled in the flues as to produce an explosive mixture, 
combustion finally occurring, the shock may be sufficient 
to cause rupture of the boiler, and, as has actually some- 
times happened, its explosion. Sewer gases have been 
known to find their way into an empty boiler through 
an open blow-off pipe, and have been exploded by the 



THE MANAGEMENT OF THE STEAM BOILER. 



127 



first light brought to the manhole, and with serious 
damage to adjacent property. Mineral oils used to 
detach scale have caused similar dangerous and some- 
times fatal explosions by the ignition of the mixture of 
their vapors and the air within the boiler. It is import- 
ant that care be taken in using lights about boilers in 
such cases of application of mineral oils. 

Explosions of gas within a boiler at work cannot 
occur ; but the suggestion of the possibility of such an 
occurrence is often made. No decomposition of water 
can take place except a portion of the boiler is over- 
heated; this happening, all the oxygen produced is 
absorbed by the iron, and no recombination can occur 
later, even were it possible for ignition to take place 
under the conditions producing decomposition. 

The flooding of a boiler with water until it is filled to 
the steam-pipe, or safety-valve, may cause so serious a 
retardation of the outflow of the mingled fluids as to 
result in overpressure and great danger. Mr. W. L. 
Gold * gives the following instances, and the experience 
of the Author justifies fully his statement. The steam- 
pipe or the safety-valve cannot relieve a full boiler rap- 
idly and safely. 

First, a boiler 38 inches in diameter, two flues, shell 
y^ inch Juniata iron, ruptured in the sheet a crack 9 
inches long, steam gauge indicating 60 lbs., safety-valve 
weighted at 80 lb. pressure. This rupture closed in- 
stantly, and if he had not seen it made, he might possi- 

*Am. Manufacturer, Feb., 1881. 



128 STEAM BOILER EXPLOSIONS. 

bly have been surprised by an explosion, with water 
and steam in their normal condition, very shortly after. 
Second, a steam-drum (spanning a battery of five boilers) 
30 inches in diameter. The blank-head forced (bulged) 
out, the 1 y 2 inch stay- rods stretched, and the corner of the 
head-flange cracked one third around. Third, a verti- 
cal boiler, built especially to carry high pressure (safe 
running pressure 150 lbs.), the hand-hole and man-hole 
joints forced out past the flanges, the steam-pipe joints 
and union forced out, the packing in the engine piston 
destroyed, and the engine generally racked, so as to be 
almost useless. Steam pressure by gauge from 40 to 
60 lbs.; safety-valve weighted at 90 lbs. 

Mr. Gold suggests that, as this is a not infrequent oc- 
currence, many explosions may be simply the final act in 
the drama commenced by the feed-pump. 

30. Emergencies must be met with a clear head 
and ready wit, with perfect coolness, and, usually, with 
both promptness and quickness of action. Every man 
employed about steam-boilers, as well as every engineer 
and every proprietor, should have carefully thought out 
the proper course to take in any and every emergency 
that he can conceive of as likely or possible to arise, and 
should have constantly in mind the means available for 
meeting it successfully. When the time comes to act, 
it is not always, or even often, possible to take time to 
study out the best thing to be done; action must be 
taken, on the instant, based on earlier thought or on 
either the intuition or the impulse of the moment. 

"Low-water" presents, perhaps, the most common, 



EMERGENCIES. 



129 



as well as one of the most serious, of such emergencies. 
The instant it is detected, the effort must be made 
to check the fall to a lower level ; the fire must be 
dampened, preferably by throwing on wet ashes, and 
the boiler allowed to cool down. Care should be taken 
that the safety-valve is not raised so as to produce a 
priming that might throw water over the heated metal, 
and that no change is made in the working of either en- 
gine or boiler that shall produce foaming or an in- 
creased pressure. If, on examination, it is found that 
the water has not fallen below the level of either the 
crown-sheet or any other extended area of heating sur- 
face, the pump may be put on with perfect safety ; but 
if this certainty cannot be assured, the boiler should be 
cooled down completely, and carefully inspected and 
tested, and thoroughly repaired, if injured. If no part 
of the exposed metal is heated to the red-heat there is 
no danger, except from a rise in the water-level and 
flooding the hot iron. If any portion should be red- 
hot, an additional danger is due to the steam-pressure, 
which should be reduced by continuing the steady work- 
ing of the engine while extinguishing the fire. If the 
safety-valve be touched at such a time, it should be 
handled veiy cautiously, allowing the steam to issue 
very steadily and in such quantities that the steam- 
gauge hand shows no fluctuation, while steadily falling. 
The damping of the fire with wet ashes will reduce the 
temperature and pressure very promptly and safely. 
The Author has experimentally performed this opera- 
tion, standing by a large outside-fired tubular boiler while 



13° 



STEAM BOILER EXPLOSIONS. 



all the water was blown out, and then covering the fire. 
The pyrometer inserted in the boiler showed no eleva- 
tion of temperature until all the water was gone, and 
the fire was then so promptly covered that the rise 
was but a few degrees and the boiler was not injured. 
As it proved, there was not the slightest danger in that 
case ; but with less promptness of action some danger 
might have arisen of injuring the boiler, although not of 
explosion. 

Overheated plates, produced by sediment, or over- 
driving, resulting in the producing of " pockets " or of 
cracks, are, virtually, cases of low- water, and the action 
taken should be the same. The boiler being safely 
cooled down, the injured plate should be replaced by a 
sound sheet, all sediment or scale carefully removed, 
and a recurrence of the causes of the accident effectively 
provided against. 

Cracks, suddenly appearing in sheets exposed to the 
fire or elsewhere, sometimes introduce a serious danger. 
The steps to be taken in such a case are the immediate 
opening of the safety-valve and reduction of steam- 
pressure as promptly and rapidly as possible, meantime 
quenching the fire and then cooling off the boiler and 
ascertaining the extent of the injury and repairing it. 
In such a case, unless the crack is near the safety-valve 
itself, no fear need be entertained of too rapid discharge 
of the steam. 

Blistered sheets should be treated precisely as in the 
case preceding. It is not always possible to surmise the 
extent of the injury or the damage involved until 



EMERGENCIES. 131 

steam is off and an examination can be made. It is not, 
however, absolutely necessary to act as promptly as in 
the preceding cases ; and, when the blister is not large 
and is not extending, it is sometimes perfectly allowable 
to await a convenient time for blowing off steam and 
repairing it. 

An inoperative safety-valve, either stuck fast, or too 
small to discharge all the steam made, or to keep the 
pressure down to a safe point, produces one of the most 
trying of all known emergencies. In such a case, steam 
should be worked off through the engine, if possible, 
and discharged through any valves available, through 
the gauge-cocks, or even through a few scattered rivet- 
holes, out of which the rivets may be knocked on the 
instant ; the fire being in the meantime checked by the 
damper, or by free use of water. The throwing of water 
into a furnace is often a somewhat hazardous operation, 
however, and, if necessary, should be performed with 
some caution, to avoid risk of injury of either the per- 
son attempting it or of the boiler. The use of wet 
ashes is preferable. In all cases in which it is to be 
attempted to reduce the rate of generation of heat, 
closing the ashpit- doors as well as opening the fire- 
doors will be of service by checking the passage of hot 
air from below and accelerating the influx of cold air 
above the grate ; but the closing of the ashpit involves, 
with a hot fire, some risk of melting down the grates. 

31. The Results of Explosions of steam-boilers, in 
spreading destruction and death in all directions, are so 
familiar as scarcely to require illustration ; but a few 



132 



STEAM BOILER EXPLOSIONS. 



instances may be described as examples in which the 
stored energy of various types of boiler has been set 
free with tremendous and impressive effect. 

Referring to the table in ^ 7, and to case No. 1 : 
The explosion of a boiler of this form and of the pro- 
portions here given, in the year 1 843, in the establish- 
ment of Messrs. R. L. Thurston & Co., at Providence, 
R. I. , is well remembered by the Author . The boiler-house 
was entirely destroyed, the main building seriously dam- 
aged, and a large expense was incurred in the purchase 
of new tools to replace those destroyed. No lives were 
lost, as the explosion fortunately occurred after the 
workmen had left the building. A similar explosion of 
a boiler of this size occurred some years later, within 
sight of the Author, which drove one end of the 
exploding boiler through a 16-inch wall, and several 
hundred feet through the air, cutting off an elm tree 
high above the ground, where it measured 9 inches in 
diameter, partly destroying a house in its further flight, 
and fell in the street beyond, where it was found red hot 
immediately after striking the earth. Long after the 
Author reached the spot, although a heavy rain was fall- 
ing, it was too hot to be touched, and was finally, nearly 
two hours later, cooled off by a stream of water from a 
hose, in order that it might be moved and inspected. 
It had been overheated, in consequence of low-water, 
and cold feed-water had then been turned into it. The 
boiler was in good order, but four years old, and was 
considered safe for 1 10 pounds. The attendant was 
seriously injured, and a pedestrian passing at the instant 









THE RESULTS OF EXPLOSIONS. 133 

of the explosion was buried in the ruins of the falling 
walls and killed. The energy of this explosion was 
very much less than that stored in the boiler when in 
regular work. 

A boiler of class No. 3, which the Author was called 
upon to inspect after explosion, had formed one of a 
" battery " of ten or twelve, and was set next the out- 
side boiler of the lot. Its explosion threw the latter 
entirely out of the boiler-house into an adjoining yard, 
displaced the boiler on the opposite side, and demolished 
the boiler-house completely. The exploding boiler was 
torn into many pieces. The shell was torn into a heli- 
cal ribbon, which was unwound from end to end. The 
furnace-end of the boiler flew across the space in front 
of its house, tore down the side of a " kier-house," and 
demolished the kiers, nearly killing the kier-house at- 
tendant, who was standing between two kiers. The 
opposite end of the boiler was thrown through the air, 
describing a trajectory having an altitude of fifty feet, 
and a range of several hundred, doing much damage to 
property en route, finally landing in a neighboring field- 
The furnace-front was found by the Author on the top of 
a hill, a quarter of a mile, nearly, from the boiler-house. 
The attendant, who was on the top of the boiler at the 
instant of the explosion, opening a steam-connection to 
relieve the boiler, then containing an excess of steam and 
a deficiency of water, was thrown over the roof of the 
mill, and his body was picked up in the field on the 
other side, and carried away in a packing-box measuring 
about two feet on each side. The cause was low- water 






! 34 STEAM BOILER EXPLOSIONS. 



and consequent overheating, and the introduction of 
water without first hauling the fires and cooling down. 
Both this boiler and the plain cylinder are thus seen to 
have a projectile effect only to be compared to that of 
ordnance. 

The violence of the explosion of the locomotive 
boiler is naturally most terrible, exceeding, as it does, 
that of ordnance fired with a charge of 150 pounds of 
powder of best quality, or perhaps 250 pounds of ordi- 
nary quality fired in the usual way. # On the occasion 
of such an explosion which the Author was called upon 
to investigate, in the course of his professional practice, 
the engine was hauling a train of coal cars weighing 
about 1000 tons. The steam had been shut off from the 
cylinders a few minutes before, as the train passed over 
the crest of an incline and started down the hill, and the 
throttle again opened a few moments before the explo- 
sion. The explosion killed the engineer, the fireman, 
and a brakeman, tore the fire-box to pieces, threw the 
engine from the track, turning it completely around, 
broke up the running parts of the machinery, and made 
very complete destruction of the whole engine. There 
was no indication, that the Author could detect, of low- 
water ; and he attributed the accident to weakening of 
the fire-box sheets at the lower parts of the water-legs 
by corrosion. The bodies of the engineer and fireman 
were found several hundred feet from the wreck, the 

* The theoretical effect of good gunpowder is about 500 foot-tons per 
pound (340 toum-metres per kilogramme), according to Noble and Able 



THE RESULTS OE EXPLOSIONS. 



135 



former among the branches of a tree by the side of the 
track. This violence of projection of smaller masses 
would seem to indicate the concentration of the energy 
of the heat stored in the boiler, when converted into 
mechanical energy, upon the front of the boiler, and its 
application largely to the impulsion of adjacent bodies. 
The range of projection was, in one case, fully equal to 
the calculated range. The energy expended is here 
nearly the full amount calculated. 




Fig. 37. — Explosion of Boilers. 
Brooklyn, N. Y. 



Figures 37, 38, 39, 40 illustrate the explosion of two 
large boilers which produced very disastrous effects,* 

* Scientific American, Mav 20, 1882. 



STEAM BOILER EXPLOSIONS. 



killing the attendant and destroying the boiler-house 
and other property. 

These boilers were horizontal, internally-fired, drop- 
flue boilers, seven feet diameter and twenty-one feet 
long, the shells, single riveted, originally five-sixteenths 
of an inch thick. 

The two exploded boilers were made twenty-one 
years before the explosion, and worked, as their makers 
intended, at about thirty pounds per square inch, until 
about twenty months before the explosion, at which 
time additional power was required, and the pressure 
was increased to, and limited at, fifty pounds. 







Fig. 38. — Position of the Three Boilers after the Explosion. 

A third boiler did not explode, but was thrown about 
fifty feet out of its bed. 

A few minutes before noon, while the engine was 
running at the usual speed, the steam-gauge indicating 
forty-seven pounds pressure, and the water-gauges show- 
ing the usual amount of water, the middle one exploded; 



THE RESULTS OE EXPLOSIONS. 



137 



the shell burst open and was nearly all stripped off. The 
remainder of the boiler was thrown high in the air. 

While this boiler was in the air, No. 1, the left-hand 
boiler, having been forcibly struck by parts of No. 2, 
also gave way, so that its main portion was projected 
horizontally to the front, arriving at the front wall of 
the building in time to fall under No. 2, as shown in 
Fig. 38. The most probable method of rupture is indi- 
cated in Fig. 38, as the line A B separates a ring of 
plates which was found folded together beneath the pile 
of debris. If the initial break had been at some point 
on the bottom, this belt of plates would have been 
thrown upward and flattened, instead of downward, 
where it was folded by the flood of water from No. 1 
boiler. 




Fig. 39. — Initial Rupture. 

The third boiler was raised from its bed by the issuing 
water, and thrown about fifty feet to the right of its 
original position. 

These two boilers contained probably more than four- 
teen tons of water, which had a temperature due to 
forty-seven pounds of steam, and the effect of its sud- 



138 



STEAM BOILER EXPLOSIONS. 



den liberation equalled that of several hundred pounds of 
exploded gunpowder. 




Fig. 40. — Interior of Boiler-House prior 
to Explosion. 

The terrible wreck usually consequent upon the ex- 
plosion of a locomotive boiler is well illustrated in the 




Fig. 41. — Exploded Locomotive. 
accompanying engraving, which represents the result cf 
such an explosion on the Fitchburg railway, August 13, 






THE RESULTS OE EXPLOSIONS, 139 

1877, while the havoc wrought among the tubes on such 
an occasion is as strikingly illustrated in the next figure. 
In the case of an explosion of a locomotive investigated 
by a commission of which the Author was a member, 
the train was moving slowly when the boiler exploded 
with a loud report ; the locomotive was turned completely 



Fig. 42. — Tubes of an Exploded Boiler. 

over backward, carrying with it the fireman, and bury- 
ing him beneath the ruins. 

Nothing could at first be found of the engineer. Par- 
ties searched for long distances about the wreck for signs 
of the unfortunate man, but it was not until next morn- 
ing that his body was found. It was discovered lying in 
the woods, seven hundred feet away from the locomo- 
tive, which was completely demolished, and every 
part of the machinery was twisted or broken into pieces. 



i 4 o STEAM BOILER EXPLOSIONS. 

The track was torn up for some distance, and rails were 
bent like coils of rope. 

The fire-box of the locomotive was hurled from its 
position and broken into many pieces. A large piece, 
weighing many hundred pounds, was carried 500 feet. 
The dome and sand-box were thrown an eighth of a mile 
into the adjacent river. The wheels of the engine were 
torn ofif, and not one piece of the cab was discovered. 
The engineer bore an excellent reputation as being a 
careful man, always carrying a large supply of water. 
The engine was one of approved make, and been in use 
for fifteen years. It had just come from the repair shop. 
A new fire-box had been put in three years before, and 
the boiler was thoroughly examined about six weeks 
earlier. The iron was, in many cases, twisted and bent 
into shapeless rolls. The point of rupture was appar- 
ently in the left hand lower corner of the outside shell of 
the fire-box. The cause was variously assigned as a 
percussive or "fulminating " action due to over-heated 
iron and to certain defective portions of the fire-box. 
The latter was probably the true cause. 

The following may be taken as another illustration 
of the tremendous effects of explosion at usual work- 
ing pressure with an ample supply of water. A boiler 
of the locomotive type was constructed for use in a small 
steamer. Its shell was of iron, 4 feet in diameter and 
5-i6th-inch thick. It was "tested" by filling with 
water and raising steam. It exploded with the safety- 
valve set at 120 pounds per square inch, blowing freely 
although held down by the man in charge, and killed 






THE RESULTS OF EXPLOSIONS. 141 

and injured several people. The hiss of steam es- 
caping from the initial rupture was heard an instant be- 
fore the explosion. The boiler was turned end for end, 
and the fire-box torn from the boiler in two pieces, one 
being carried to a distance of about five hundred feet and 
imbedded in the mud of a canal bed ; the other portion, 
weighing about 4,800 pounds, was carried a distance of 
between 400 and 500 feet, and crashed into the side of 
a building, and with sash, blinds and doors, piled closely 
together. One piece of iron comprised the fire-box, 
the dome, and the end of the boiler, and was straightened 
into a piece 30 feet long and four feetwide. The piece is 
said to have rushed through the air with a whirling motion 
until it struck the building. It cut the side of the build- 
ing and beams and rafters like straws, pushing the front 
of the building forward several feet. Fragments of the 
boiler were found at many points considerably distant 
from the scene of the explosion, and in many places win- 
dows were shattered by the concussion. 

The shell of the boiler was reversed by the force of the 
explosion, with such force that one end was buried four 
feet in the road bed. All the flues remained in the boiler, 
one end of which was torn from them while the other re- 
mained in place. 

At the instant of the explosion the air for many feet 
in every direction was filled with flying fragments, many 
of them being thrown to a great height. 

In one case coming under the observation of the 
Author, a locomotive set as a stationary boiler gave way 
in the fire-box, and let out the water and steam, but in- 



142 



STEAM BOILER EXPLOSIONS. 



Dnp- 



juring no one. The rent was about twelve inches long 
and eight inches wide. The iron in that place was weak- 
ened by corrosion, otherwise the boiler was in good con- 
dition. Repairs were immediately commenced and the 
boiler was ready for use next day. Had this rent oc- 
curred at or above the water-level, it is very possible that 
an explosion may have resulted in the manner suggested 
by Clark and Colburn. 

In an explosion of a tubular boiler at Dayton, O., 
October 25th, i88i, # by which several lives and much 
property were destroyed, the rupture started along the 
lap A B in the figure, and was evidently due to the 






Fig. 43. — Initial Rupture ; "Grooving." 

furrowing which had been there, in some way, produced. 
The boiler was less than a year old, and was reported 
to be of good material and workmanship. The longi- 
tudinal seams were double-riveted, and it is very possi- 
ble that the stiffness thus produced along their lines 
may have so localized the strains due to alterations of 



* Scientific American, Dec. 17th, 1881. 



THE RESULTS OF EXPLOSIONS. 



143 



form as to have led to this fatal result, aided by the 
action of the caulking tool, the marks of which, along 
the lines at which the crack gradually worked through 




Fig. 44. — Boiler Explosion at Dayton, 
Ohio. 

the sheet, are plainly visible. The boiler had, when 
first set in place, been tested to 140 pounds; the explo- 
sion occurred at probably less than 80. 




Fig. 45. — Girdle of Plates 
from No. 2 Boiler. 

A strip of plates, as in the above figure, was torn 
from the boiler, separating it into two parts, as seen in 



144 



STEAM BOILER EXPLOSIONS. 




Fig. 46. — Rear End op Boiler After Ex- 
plosion. Rear End of Boiler Before 
Explosion. 

the two succeeding figures, and throwing them apart 







Fig. 47. — Front End of Boiler 
after Explosion. 



with all the force due to a hundred millions of foot- 




5.— Principal part of.No. 5 boiler thrown over the church on the bluff. 
6. — Principal part of No. 6 boiler. 

Fig. 48. — Explosion of two Steam Boilers at Pittsburg, Pa. 



THE RESULTS OE EXPLOSIONS. I45 

pounds of available stored heat-energy, entirely de- 
stroying the house in which they were set. 

In a case of explosion at Pittsburg, Pa., in December, 
1 88 1, a battery of flue-boilers was connected, as seen in 
the figure, by steam-drums above the nearer two and 




Fig. 49.— Under Sides of Boilers. 

mud-drums beneath all three. The steam-pressure was 
not far from 125 pounds per square inch at the time of 
the accident. The boilers were fifteen years old, but 
had been tested to 170 pounds two years earlier, and 
allowed to work at 120 pounds, although they had been 
repeatedly patched and repaired.* The rules of the 
insurance companies would have allowed but one-half 
this pressure. 

The strains produced by the changes of form with 
varying temperature of feed- water, and by the action 
of the new iron of the patches on the older and corroded 
parts of the boilers, started cracks which gradually 
weakened them, and finally led to a rupture along the 
worst line of injury, A B> in the preceding figure, open- 
ing the course of plates at a> and tearing it out as in 

* Scientific American, Feb. 4, 1882. 



146 



STEAM BOILER EXPLOSIONS. 






the next figure, in which A £ is the line of initial frac- 
ture. The destruction of this (No. 6) boiler was accom- 
panied by the disruption of that next to it (No. 5), 
which was also in about as dangerous condition. The 
available energy of the explosion was about 250,000,000 




Fig. 50. — Course of Plates Detached. 
foot-pounds, and the damage produced was proportioned 
to this enormous power. 

One boiler (No. 5) was thrown across the road and 
over a church ; the other (No. 6) was thrown to one 




Fig. 51.— Piece of " Patch." 
side, partially destroying neighboring buildings. The 
boiler-house was entirely destroyed. The third boiler 
remained unexploded and was found a little out of place 
and nearly full of water. 



_ 



THE RESULTS OE EXPLOSIONS. 



147 



According to the observer furnishing these particulars, 
the conclusions are inevitable : 

That the two boilers exploded in succession so quickly 
as to be practically simultaneous, beginning at the weak 
line A B of No. 6 boiler; 

That they contained an ample supply of water; 

That the pressure was too great for boilers of their 
size and condition. 

That the use of cold feed-water hastened the deterio- 
ration of poor iron, causing cracks and leaks, by which 
external corrosion was produced, and that the energy 
stored in the water of these boilers caused all the 
destruction observed. 

It is always to be strongly recommended that regular 
and continuous feeding of hot water be practiced; and 
that the greatest care be exercised by inspectors and 
those in charge of steam-boilers in searching for and 
immediately repairing dangerous defects. 

The last figure, preceding, is an excellent illustration 
of the appearance of iron when thus corroded. At C, 
the crack was old and partly filled up with lime scale. 

The explosion of the upright tubular- boiler is usually 
consequent upon some injury of its furnace, either by 
collapse or by the yielding of the tube-sheet to exces- 
sive pressure. The result is commonly the projection 
of the boiler upward like a rocket, and is rarely accom- 
panied by much destruction of property laterally. A 
typical case of this kind is that of an explosion occur- 
ring at Norwich, Connecticut, December 23, 1881, of 
which the following is a brief account:* 

* Scientific American, Jan. 14, 1SS2- 



148 



STEAM BOILER EXPLOSIONS, 







Fig, 52. — Explosion of an Upright Boiler. 

Fig. 53 represents the location of the boiler and 
engine immediately before the explosion. The explo- 
sion took place, as shown in figure by the yielding of 
the lower tube plate of the boiler. 

This boiler was three feet in diameter and seven feet 
high. The boiler was made of five-sixteenths iron 
throughout. It contained sixty tubes, two inches diam- 
eter, five feet long, which were set with a Prosser ex- 
pander, and were beaded over as usual. The upper tube- 
head wns flush with the top of the shell, and the lower, 
forming the crown of the furnace, was about two feet 
above the grates and thebase of the shell, and was flanged 
upon the inner surface of the furnace. There was a 
safety plug in the lower tube-head, which was not melted 
out, although, as is often the case when these plugs are 



THE RESULTS OE EXPLOSIONS. 



149 



so near the fire, a portion of the lower part of the fusible 
filling had disappeared. 




Fig. 53. — The Boiler Room Before the Explosion. 

The working pressure was sixty pounds per square 
inch, and the explosion probably took place at or a little 




Fig. 54. — Yielding Tube Sheet. v 

below this pressure, throwing the boiler through the roof 
and high over a group of buildings and a tall tree close 



i5° 



STEAM BOILER EXPLOSIONS. 



by, finally burying itself half its diameter in the frozen 
ground. 




Fig. 55. — The Exploded Botler. 

There had been leaks in the tubes and four had been 
plugged. There was a crack in the upper head near the 
center which extended between three tubes. From this 
crack steam escaped, and the water had settled upon the 
surrounding surface of the tube-head and the tube-ends. 
The result was to reduce the five-sixteenths plate to less 
than a quarter of an inch in thickness, and the tube-ends 
to the thickness of writing paper. The lower tube-ends 
had suffered still more from leaks and were as thin as paper 
and afforded no adequate support to the head. The 
pressure consequently forced the lower head down, open- 
ing fifty or more holes, two inches diameter, from which 
the fluid contents of the boiler issued at a high velocity, 
and the whole boiler became a great rocket weighing 
about two thousand pounds. 



THE RESULTS OE EXPLOSIONS. 



I 5 I 



One life was destroyed by this explosion and a con- 
siderable amount of property. 

An explosion which occurred at Jersey City, N. J., 
some years ago, illustrated at once the dangers of low- 
water and of a safety-valve rusted fast. As reported at 
the time : # " The boiler was of the locomotive type, 
having a dome upon the top. The engineer upon the 




Fig. 56. — The Explosion. 
morning of the explosion lighted the fire in the boiler 
and shortly afterward was called away, leaving the boiler 
in charge of his nephew, who was young and inexperienced 
in the handling of steam. After putting fresh coal in 
the furnace he was called away by one of the owners of 
the dock to assist at some outside duty. Upon his re- 



*Am. Machinist, Oct. 1st, 1881. 



[52 STEAM BOILER EXPLOSIONS. 



turn he saw the seams of the boiler opening, and attempte 
to open the furnace door, but was unable, owing to the 
excess of pressure of steam within the boiler which had 
caused the head to change its shape. A few moments 
afterward the explosion occurred. The fire-box being 
thrown downward, the top of the shell and crown-sheet 
upward, while the cylinder part shot directly up the 
street. It struck the ground about 400 feet from its 
original position, demolished afire hydrant, several trucks, 
trees, and a horse, and, spinning end for end, came to 
rest by the side of a truck, which it destroyed, about 
642 feet from its starting point. Subsequent investiga- 
tion revealed the fact that the boiler was not properly 
supplied with water. A portion of the crown sheet 
which we examined showed conclusively that near the 
flues it was red-hot. We also examined the safety-valve, 
which was of the wing pattern, having a lever and weight. 
This valve was so firmly corroded to its seat that it could 
not be removed, and the stem was also corroded fast. 
The whole secret of this explosion is that the boiler was 
short of water and an excessively high pressure of steam 
was raised to an unknown point ; which, without relief, 
acquiring sufficient force, tore the boiler to pieces. ,, 

The valve was found and, being placed in a testing 
machine then under the charge of the Author, at the 
Stevens Institute of Technology, was only started by a 
pressure of a ton and a half; # while nearly two tons 
was required to move it observably. 

*Ibid, Oct. 22d, 1881. 



. 



THE RESULTS OF EXPLOSIONS. 



*S3 



Change of form with varying pressures and tempera- 
tures sometimes produces most unexpected defects. It 




Fig. 57. — Faulty Staying. 

has been observed that many locomotive boilers stayed 
as in the figure, * give way at the side, in the manner 
here exhibited. Investigation shows that, in these cases, 
the tying of the furnace-crowns to the shell by the sys- 
tem of staying illustrated, and the continual rising and 
falling of the furnace relatively to the shell, is very apt to 
cause a buckling of the outside sheet along the horizontal 
seam, which finally yields. This buckling and straight- 
ening of the sheet goes on until a crack or a furrow is 
formed along the lap nearest the most rigid brace, and, 
when this has cut deeply enough, the side of the boiler 
opens, often the whole length of the furnace, the ex- 
plosion doing an amount of damage which is determined 

* Locomotive, Jan. 1, 1880. 



154 



STEAM BOILER EXPLOSIONS. 



by the steam pressure, the quantity of energy stored, and 
the extent of the rupture. 







Fig. 58. — Collapsed Flues. 

In these cases, either the crown-bars over the furnace, 
or the stays, should alone have been used ; their use to- 




Fig. 59. — Collapsed Flues. 

gether is objectionable. Of the two systems, probably 
the first is safest in such boilers. 

The appearance of a collapsed flue is seen in the two 



THE RESULTS OF EXPLOSIONS. 155 

succeeding figures, which represent the results of experi- 
ments made by the U. S. Commission appointed to 
investigate the causes of explosions of steam boilers. 
In neither case did the boiler move far from its original 
position. Collapsed flues rarely cause extensive destruc- 
tion of property. 

An explosion of a rotary rag-boiler, receiving steam 
from steam-boilers at a distance, which took place at 
Paterson, N. J., wrecked the mill, destroyed a part of 
an adjacent establishment, and caused serious loss of 
life and property. The disaster was due to the weak- 
ening of the boiler by corrosion, but, notwithstanding 
its reduced strength, the shock of the explosion was 
felt, and was heard, throughout the city, and heavy 
plate-glass windows were broken at a considerable dis- 
tance from the scene of the accident. Explosions of 
this kind show the fallacy of many of the absurd and 
mischievous " theories" which have been prevalent in 
regard to explosions. 

Where the iron or steel used in the construction of the 
boiler is of good quality, strong, uniform and ductile, 
the smaller torn parts of an exploded boiler may not 
break away from the main body ; such a case is illus- 
trated in the accompanying figure, which represents the 
effect of an explosion of a new boiler from a cause not 
ascertained. 

The boiler was 15 feet long by 4 feet diameter, with 
38 four-inch flues. Both heads remained on the flues, 
but the shell of the boiler burst along the rivet holes 
nearly all around both heads, as shown in the engraving. 



iS6 



STEAM BOILER EXPLOSIONS. 



32. Experimental Investigations of the causes and 
methods of steam-boiler explosions have been occasion- 
ally attempted. One of the earliest and most syste- 



Fig. 60. — An Exploded Boiler. 

matic, as well as fruitful, was that of a Committee of the 
Franklin Institute, the results of which were reported to 
the Secretary of the U. S. Treasury, early in 1836. 

Unpublished experiments recently made by Professor 
Mason at the Rensselaer Polytechnic Institute, strongly 
confirm the so-called " geyser theory " of Messrs. Clark 
and Colburn. In these experiments a number of mina- 
ture boilers were constructed, and were exploded by a 
gradually produced excess of pressure, and in such 
manner as to test this theory. The first of these boilers, 
when exploded, produced such an effect, blowing out 
windows and shaking down the ceiling of the laboratory 
as effectually to dispose of the idea prevalent among 
certain classes of engineers, that a true explosion could 
only be caused by low-water and overheated plates. 
Another boiler was so set that, the rear end being lower 
than the front, the quantity of water acting by percus- 






EXPERIMENTAL INVESTIGA TIONS. 1 5 7 

sion, according to the Clark theory, was much greater 
at the one end than at the other. The consequence was 
that, while the one end was broken into many pieces, 
that in which there was least water was simply torn 
from the mass of the boiler and was itself unbroken. 
In one of this series of experiments the boiler was 
broken into more than a hundred pieces, although 
made of drawn brass, a material far less liable, ordina- 
rily, to be thus shattered than iron or steel. The second 
of the above described experiments appears to the 
Author a very nearly crucial test and proof of the 
theory of Messrs. Clark and Colburn. 

The Franklin Institute committee proposed by ex- 
periments : 

(I). To ascertain whether, on relieving water heated 
to, or above, the boiling point, from pressure, any com- 
motion is produced in the fluid. 

To determine the value of glass gauges and gauge- 
cocks. 

The investigation of the question whether the elasti- 
city of steam within a boiler may be increased by the 
projection of foam upon the heated sides, more than it 
is diminished by the openings made. 

(II). To repeat the experiments of Klaproth on the 
conversion of water into steam by highly heated metal 
and to make others, calculated to show whether, under 
any other circumstances, intensely heated metal can 
produce, suddenly, great quantities of highly elastic 
steam. 

To directly experiment in relation to the production 



158 S TEAM BOILER EXPLOSIONS. 

of highly elastic steam in a boiler heated to high temper- 
ature. 

(III). To ascertain whether intensely heated and un- 
saturated steam can, by the projection of water into it, 
produce highly elastic vapor. 

(IV). When the steam surcharged with heat is pro- 
duced in a boiler, and is in contact with water, does it 
remain surcharged, or change its density and tempera- 
ture ? 

(V). To test, by experiment, the efficacy of plates, 
etc., of fusible metal, as a means of preventing the undue 
heating of a boiler, or its contents. 

(1). Ordinary fusible plates and plugs. 

(2). Fusible metal, inclosed in tubes. 

(3). Tables of the fusing points of certain alloys. 

(VI). To repeat the experiments of Klaproth, &c. 

(1). Temperature of maximum vaporization of copper 
and iron under different circumstances. 

(2). The extension to practice, by the introduction of 
different quantities of water, under different circum- 
stances of the metals. 

(VII). To determine by actual experiment, whether 
any permanently elastic fluids are produced within a 
boiler when the metal becomes intensely heated. 

(VIII). To observe accurately the sort of bursting 
produced by a gradual increase of pressure, with cylin- 
ders of iron and copper. 

(IX). To repeat Perkins' experiment and ascertain 
whether the repulsion stated by him to exist between 
the particles of intensely heated iron and steam be gen- 



EXPERIMENTAL INVESTIGATIONS, 



[ 59 



eral, and to measure, if possible, the extent of this re- 
pulsion, with a view to determine the influence it may 
have on safety-valves. 

(X). To ascertain whether cases may really occur 
when the safety-valve, loaded with a certain weight, re- 
mains stationary, while the confined steam acquires a 
higher elastic force than that which would, from calcu- 
lation, appear necessary to overcome the weight of the 
valves. 

(XI). To ascertain by experiment the effects of de- 
posits in boilers. 

(XII). Investigation of the relation of temperature and 
pressure of steam, at ordinary working pressures. 

It is only necessary here to state that the result 
proved : 

(i). That relieving pressure, even slightly, produced 
great commotion in the water, and considerably reliev- 
ing it caused the violent ejection of water as well as 
steam through the opening by which the pressure was 
reduced. 

(2). That under similar conditions pressure invariably 
diminished. 

(3). That the injection of water upon the heated sur- 
faces of the experimental boiler, produced a sudden and 
considerable rise of pressure. 

(4). That the injection of water into superheated steam 
reduced its pressure. 

(5). That superheated steam may remain in contact 
with water a long time (two hours in the experiments 
tried), without becoming saturated, 



j6o steam boiler explosions. 

(6). That fusible plugs, as then constructed, were un- 
reliable. The fusing point of various alloys were de- 
termined. 

(7). That the temperature of maximum vaporization 
of water is lowered by smoothness of surfaces ; that that 
of iron is thirty or forty degrees higher than that of cop- 
per, while the time required is one-half as great with 
copper; that the temperature of maximum vaporization, 
for oxidized iron, or for highly oxidized copper is about 
350 F., and that the repulsion between the metal and 
the water is perfect at from twenty to forty degrees above 
the temperature of maximum vaporization. 

(8). That no hydrogen is liberated by throwing water 
or steam upon heated surfaces of the boiler; that 
the water was not decomposed, and that air cannot oc- 
cur in any appreciable quantity in a steam-boiler at work. 

(9). That " all the circumstances attending the most 
violent explosions may occur without a sudden increase of 
pressure within a boiler" the explosion being produced 
by gradually accumulated pressure. 

(10). That but a small portion of water, highly heated, 
can expand into steam, if suddenly relieved of pressure. 

(n). That water can be heated to very high temper- 
ature only under immensely high pressure. 

(12). That steam-pressure may rise even after it has 
raised the safety-valve. 

Over thirty years passed before another serious at- 
tempt was made to thoroughly investigate the subject; 



EXPERIMENTAL INVESTIGATIONS. 



161 



but in the year 1871, experiments were inaugurated on a 
large scale.* 

In the work of investigation involving the explosion 
of steam-boilers, it is usually necessary to provide a safe 
retreat for the observers, from which to watch the pro- 
gress of the experiment, and from which to read the 
steam-gauge, to watch the water-level, and to take the 
reading of the thermometers or pyrometers. 




Fig. 61. — Bomb-proof. 

The illustration represents the structure, composed of 
heavy timber, and partially underground, used at the 
testing ground at Sandy Hook, by the U. S. Commis- 
sion of 1873-6. 

These experiments were projected and conducted by 
Mr. Francis B. Stevens, of Hoboken, and at the request of 
Mr. S. the United Railroad Companies of New Jersey 
appropriated the sum of ten thousand dollars to enable 
Mr. Stevens to enter upon a preliminary series of ex- 



* Journal Franklin Inst., Jan., 1872, 



!6 2 steam boiler explosions. 

periments. They, at the same time, invited other rail- 
roads and owners of steam-boilers to co-operate with 
them, and offered the use of their shops for any work 
that might be considered necessary or desirable during 
the progress of the work; no such aid was, however, re- 
ceived. 

Several old boilers had recently been taken out of the 
steamers of the United Companies. These were sub- 
jected to hydrostatic pressure, until rupture occurred, 
were repaired and again ruptured several times each, thus 
detecting and strengthening their weakest spots, and 
finally leaving them much stronger than when taken from 
the boats. The points at which fracture occurred and 
the character of the break were noted carefully at each 
trial. 

After the weak spots had thus been felt out and 
strengthened, the boilers were taken, with the permis- 
sion of the War Department, to the U. S. reservation at 
Sandy Hook, at the entrance to New York Harbor, and 
were there set up in a large enclosure which had been pre- 
pared to receive them, and the four old steamboat boilers 
above referred to, together with five new boilers built for 
the occasion, were placed in their respective positions 
without having been in any way injured. 

Finally, on the 22d and 23d of November, the exper- 
iments to be described were made. 

The first boiler attacked was an ordinary " single return 
flue boiler." 

The cylindrical portion of the shell was 6 feet 6 inches 
diameter, 20 feet 4 inches long, and of iron a full quarter 






EXPERIMENTAL INVESTIGA TIONS. 



163 



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Fig. 62.— Marine Boiler. 

inch thick. The total length of the boiler was 28 feet, 
the steam chimney was 4 feet diameter, 10^ feet high 
and its flue was 32 inches diameter. The two furnaces 
were 7 feet long, with flat arches. There were ten 
lower flues, two of 16 and eight of 9 inches diameter 
and all were 1 5 feet 9 inches long ; there were twelve 
upper flues, Z]/ 2 inches in diameter, and 22 feet long. 
The total grate surface was 38^ square feet, heating sur- 
face 1350 square feet. The water spaces were 4 inches 
wide, and the flat surfaces were stayed by screw stay- 
bolts at intervals of 7 inches. The boiler was thirteen 
years old, and had been allowed 40 pounds pressure. 

The upper portion of the boiler, when inspected before 
the experiment, seemed to be in good order. The girth 



164 



STEAM BOILER EXPLOSIONS. 



seams on the under side of the cylindrical portion had 
given way, and had all been patched before it was taken 
out of the boat. The water legs had been considerably 
corroded. 

In September this boiler had been subjected to hy- 
drostatic pressure, giving way by the pulling through 
of stay-bolts at 66 pounds per square inch. It was re- 
paired and, afterward, at Sandy Hook, was tested without 
fracture to 82 pounds, and still later bore a steam pres- 
sure of 60 pounds per square inch. 

On its final trial, Nov. 22d, a heavy wocd fire was 
built in the furnaces, the water standing 1 2 inches deep 
over the flues, and, when steam began to rise above 50 
pounds, the whole party retired to the gauges, which were 
placed about 250 feet from the enclosure. The notes of 
pressures and times were taken as follows : 






Time. Pressure. 



2.00 P.M. 
2.05 '* 
2.10 M 



58 lbs. 
68 " 
78 " 



Time. Pressure. 



2.15 P.M. 
2.20 " 

2.23 " 



87 lbs. 

93 



Time. Pressure. 



2.25 P.M. 91^ ^s. 
2.36 4k 91 " l 
2-35 " 9 J K " 



Time. Pressure, 



2.40 P.M. 
2.50 



91^ lbs. 

91 " 

90 



The pressure rose rapidly until it reached about 90 
pounds,* when leaks began to appear in all parts of the 
boiler, and at 93 pounds a rent at A, (Fig. 62) the lower 
part of the steam chimney where it joins the shell becom- 
ing quite considerable, and other leaks of less extent en- 



* The ultimate strength of this boiler, when new, was probably equal 
to about double this pressure. 



EXPERIMENTAL INVESTIGA TIONS. 



165 



larging, the steam passed off more rapidly than it was 
formed. The pressure then slowly diminishing, the 
workmen extinguished the fires by throwing earth upon 
them, and the experiment thus ended. 

The second experiment was made with a small boiler 



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Fig. 63. — Stayed Water Space. 

(Figure 63) which had been constructed to determine 
the probable strength of the stayed-surface of a marine 
boiler. It had the form of a square box, 6 feet long, 4 
feet high, and 4 inches thick. Its sides were 5 inch 
thick, of the " best flange fire-box" iron. The water- 
space was 3^ inches wide. The rivets along the edges 
were ^ inch diameter, spaced 2 inches apart. The two 
sides were held tegether by screw stay-bolts, spaced 8^ 
and 9i 3 6 inches, and their ends were slightly riveted 
over, precisely copying the distribution and workman- 
ship of a water-leg of an ordinary marine boiler It had 
been tested to 138 lbs. pressure. This slab was set in 
brickwork, about five-sixths of its capacity occupied by 
water, and fires built on both sides. Pressure rose as 
shown by the following extract from the note-book of 
the Author : 






1 66 



STEAM BOILER EXPLOSIONS. 



Time. P 


ressure. 


Time. 


Pressure. 


Time. 


Pressure. 


Time. Pressure. 


3.18 P.M. 


lbs. 


3.27 P.M. 18 lbs. 


3-35 P.M 


49 lbs. 


3.43 P. M. 94 lbs' 


3.20 ' 


4 ' 


3.28 


20 


3-3 6 


5i " 


3.44 ( 100 




3 ' 21 u 


5 ' 


329 


23 !! 


3-37 


54 , 


3-45 ' no 


4 


3.22 


7 


3-30 


27 


3.38 


f 


3.46 ; 117 




3.23 


9 


3-3i 


30 ; 


3-39 ' 


65 " 


3.47 ' 126 


4 


3.24 


11 


3.32 


34 > 


3-40 


7 o < 


3-48 • 135 


4 


3 - 2 ! i« 


13 " 


3-33 


38 


3.4i 


78 " 


3.49 147 


4 


3.26 M 


15 


3.34 


44 " 


3.42 " 


86 " 


3.50 160 


4 














3.51 " 165 •■ 














Exploded. 



At a pressure of slightly above 165, and probably at 
about 167 pounds, a violent explosion took place. 
The brickwork of the furnace was thrown in every 
direction, a portion of it rising high in the air and fall- 
ing among the spectators near the gauges ; the sides of 
the exploded vessel were thrown in opposite directions 
with immense force, one of them tearing down the high 
fence at one side of the enclosure, and falling at a con- 
siderable distance away in the adjacent field ; the other 
part struck one of the large boilers near it, cutting a 
large hole, and thence glanced off, falling a short dis- 
tance beyond. 

Both sides were stretched very considerably, assum- 
ing a dished form of 8 or 9 inches depth, and all of the 
stay-bolts drew out of the sheets without fracture and 
without stripping the thread of either the external or the 
internal screw; this effect was due partly to the great 
extension of the metal, which enlarged the holes, and 
partly to the rolling out of the metal as the bolts drew 
from their sockets in the sheet. 

Lines of uniform extension seemed to be indicated by 
a peculiar set of curved lines cutting the surface scale of 
oxide on the inner surface of each sheet, and resembling 



EXPERIMENTAL INVESTIGATIONS. 167 

closely the lines of magnetic force called, by physicists, 
magnetic spectra. These curious markings surrounded 
all of the stay-bolt holes. 

The third experiment took place on the 23d of No- 
vember. The boiler selected on this occasion was a 
"return tubular-boiler, ,, with no lower flues; the furnace 
and combustion-chamber occupying the whole lower 
part. Its surface extended the whole width of the 
boiler, thus giving an immense crown-sheet. 

This boiler was built in 1 845, and had been at work 
twenty -five years ; when taken out, the inspector's cer- 
tificate allowed 30 lbs. of steam. In September it was 
subjected to hydrostatic pressure, which at 42 pounds 
broke a brace in the crown-sheet, and at 60 pounds, 12 
of the braces over the furnace gave way, and allowed 
so free an escape of water as to prevent the attainment 
of a higher pressure. The broken parts were carefully 
repaired, and the boiler again tested at Sandy Hook to 
59 lbs., which was borne without injury, and afterward 
a steam-pressure of 45 lbs. left it still uninjured. At 
the final experiment, the water level was raised to the 
height of 15 inches above the tubes, and it there 
remained to the end. The fire was built, as in the pre- 
vious experiments, with as much wood as would burn 
freely in the furnace, and the record of pressures was as 
follows : 



Time. Pressure. 



12.21 P.M. 29^ lbs. 
12 -23 '* 33^ " 
l2 -25 " 37^ " 



Time. Pressure. 



12.27 P.M. 41 lbs. 
12.29 " 44K ' 
12.31 *• 48M " 



Time. Pressure. 



12.32 P.M. 50 lbs., brace broke. 

12.33 52 " 

12.34 " 53K exploded. 



1 68 • STEAM BOILER EXPLOSIONS. 

In these second and third experiments, we have illus- 
trations of the comparatively rare cases in which explo- 
sions actually occur. 

The second was a perfectly new construction, in 
which corrosion had not developed a point of great 
comparative weakness, and the edges yielding along the 
lines of riveting on all sides simultaneously and very 
equally, the two halves were completely separated, and 
thrown far apart with all of the energy of unmistakable 
explosion, although there was an ample supply of water, 
and the pressure did not exceed that frequently reached 
in locomotives and on the western rivers, and although 
the boiler itself was quite diminutive. 

In the third experiment, as in the second, it is prob- 
able that the weakest part extended very uniformly over 
a large part of the boiler, either in lines of weakened 
metal, or over surfaces largely acted upon by corrosion. 
Immediately upon the giving way of its braces, frac- 
ture took place at once in many different parts. 

33. Conclusion. We may conclude, then, from 
the result of Mr. Stevens' experiments: 

First. — That " low- water," although undoubtedly one 
cause, is not the only cause of violent explosions, as is 
so commonly supposed, but that a most violent explo- 
sion may occur with a boiler well supplied with water, 
and in which the steam-pressure is gradually and slowly 
accumulated. 

This was shown on a small scale by the experiments 
of the Committee of the Franklin Institute above 
referred to. 



EXPERIMENTAL INVESTIGATIONS. 169 

Second. — That what is generally considered a moderate 
steam-pressure may produce the very violent explosion 
of a weak boiler, containing a large body of water, and 
having all its flues well covered. 

This had never before been directly proven by ex- 
periment. 

Third. — That a steam-boiler may explode, under 
steam, at a pressure less than that which it had success- 
fully withstood at the hydrostatic test. 

The last boiler had been tested to 59 lbs., and after- 
ward exploded at 53 ^ lbs. This fact, too, although 
frequently urged by some engineers, was generally dis- 
believed. It was here directly proven.* 

In addition to the deductions summarized above, the 
Author would conclude : 

Fourth. — That the violence of an explosion under 
gradually accumulating pressures is determined largely 
by the nature of the injury and the extent of the pri- 
mary rupture due to it. A merely local defect or failure 
would not be likely to cause explosion. 

* A number of instances of this kind, though not always producing- an 
explosion, have been made known to the Author. Two boilers at the 
Detroit Water Works, in 185Q, after resisting the hydrostatic test of 
200 lbs. with water, at a temperature of ioo° Fahr., broke several braces 
each at no and 115 lbs. steam pressure respectively, when first tried 
under steam. The boiler of the U. S. steamer Algonquin was tested with 
150 lbs. cold water-pressure, and broke a brace at 100 lbs. when tried 
with steam. A similar case occurred in New York, a few years ago, and 
the boiler exploded with fatal results. These accidents are probably 
caused by the changes of form of the boiler, under varying temperature, 
which throw undue strain upon some one part, which may have already 
been nearly fractured. 



170 STEAM BOILER EXPLOSIONS. 

Fifth. — That the overheating of the metal of a boiler 
in consequence of low- water may, or may not, produce 
explosion, accordingly as the sheet is more or less 
weakened, or as the amount of steam made on the over- 
flow of the dry heated area by water is greater or less. 

Sixth. — That the superheating of either water or 
steam is not to be considered a probable cause of ex- 
plosion. 

Seventh. — That the question whether the repulsion of 
water from a plate by the overheating of the latter may 
occur with resulting explosion remains unsettled, but 
that it is certain that the number of explosions attrib- 
utable to this cause is comparatively small. 

Eighth. — That all explosions are certainly due to 
simple and preventable causes, and nearly all to simple 
ignorance or carelessness, on the part of either designer, 
constructor, proprietor, or attendants. 

A Committee of the British House of Commons 
after long study and careful investigation of this subject, 
made the following recommendations : 

" 13. (a) That it be distinctly laid down by statute 
that the steam-user is responsible for the efficiency of 
his boilers and machinery, and for employing competent 
men to work them ; (b) that, in the event of an explo- 
sion, the onus of proof of efficiency should rest on the 
steam-user ; (c) that in order to raise prima facie proof, 
it shall be sufficient to show that the boiler was at the 
time of the explosion under the management of the 
owner or user, or his servant, and such prima facie 
proof sha 1 l only be rebutted by proof that the accident 



EXPERIMENTAL INVESTIGA TIONS. i y , 

arose from some cause beyond the control of such 
owner or user ; and that it shall be no defence in an 
action by a servant against such owner or user being his 
master, that the damage arose from the negligence of a 
fellow servant." 

The Prevention of steam-boiler explosions is now 
seen to be a matter of the utmost simplicity. A well 
designed, well made and set, and properly managed 
steam-boiler may be considered as safe. Explosions 
never occur in such cases. To secure correct design 
and proportions, a competent engineer should be found 
to make the plans; to obtain good construction, a reli- 
able, intelligent and experienced maker must be entrusted 
w r ith the construction under proper supervision and pre- 
cise instructions from the designer ; and the latter should 
also attend carefully to the installation of the boiler. 
In order to insure good management, trustworthy, skill- 
ful, and experienced attendants must be found, who, 
under definite instructions, may at all times be depended 
upon to do their work properly. Periodical inspection, 
prompt repair of all defects when discovered, and the 
removal of the boiler before it has become generally 
deteriorated and unreliable, are absolute safeguards 
against explosion. 



INDEX. 



ART. PAGE 

Boilers, 

energy stored in 7 23 

explosions, statistics of , 11 41 

management of 29 125 

relative safety of 22 98 

Bursting, explosion distinguished from 9 34 

Calculations of Energy; deductions from 4 12 

Causes of Explosions 10 36 

colburn and clark's theory of explosions 13 49 

Conclusions; preventives of explosions 33 168 

Constructions; defective 24 105 

Curves of Energy 5 15 

Decay, general and local. ... 26 114 

methods of 27 117 

Design, defective 23 100 

Emergencies 30 

Energy, 

calculated quantity of 3 8 

character of 6 17 

curves of 5 15 

deductions from calculations of 4 12 

formulas for stored 2 4 

in heated metal 15 61 

in super-heated water 19 78 

of steam alone 8 32 

stored in steam boilers 7 23 

stored, of fluid 1 3 

172 



INDEX. Ff2 

Explosions, 

causes of 10 36 

distinguished from bursting 9 34 

experimental investigations of 32 156 

preventives of 33 168 

results of 3 41 

statistics of boiler 11 3 

Fluid, stored energy of 2 3 

Formulas, for energy stored 2 4 

Incrustation, sediment and 18 73 

Investigation, experimental 32 156 

Low Water and Consequences 17 63 

Management of Boilers 29 125 

Metal, 

energy in heated 15 61 

resistance of heated.. 16 63 

Methods, theories and, of explosions. 12 47 

Pressure, steady increase of. 21 94 

Preventives of Explosions 33 168 

Safety, relative, of boilers 22 98 

Sediment and Incrustations 18 73 

Spheroidal State of Water 20 86 

Statistics of Boiler Explosions n 41 

Steam Alone, energy of 8 122 

Temperature Changes ' 28 122 

Theory, Colburn and Clark's 13 49 

Theories and Methods of Explosions 12 47 

Water, 

energy in super-heated 19 78 

low, and its effects , 17 63 

spheroidal state of 20 36 

Weakness, developed... . ... 25 ico 




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